Vintage speaker upgrade suggestions?

To start it off... I'm one of those people who's trying to go hifi on a very very low budget. My find of the year was a Marantz SR2000 receiver (circa 1970+?) and a pair of Mission 710's (bookshelves, 1983+) for $100. Recently, I came across an ad for a pair of Boston Acoustics A70's for $30. My questions are as follows. The receiver is rated at 40 watts per channel. Will this be enough to adequately power the A70's? If so, how big of a difference in sound will I get? I also have the option of using these to replace a pair of Bose 401's attached to a different receiver. Lastly, I couldn't really get a straight answer out of the guys at Myer Emco when I asked whether I'd notice any difference if I were to listen to SACDs using this system. I was told "some people can hear a difference, some people can't" implying there's not a real difference.

In summation:
Is 40w/channel enough to power A70's?
How do A70's compare against Mission 710's or Bose 401's?
Would I notice any advantages in switching to SACD with these speakers/receiver?

If it helps, I listen to Jazz (mostly vocal), Classical (mostly piano) and a bit of electronic.
Forget about SACD!

Please don't take this the wrong way, but you will not get hi-end sound from your buying methods. But if you find that you enjoy the sound, then you are lucky, because you will not catch the "audiophile addiction", which can be quite expensive.

First, the Marantz is about 25 years old, and should be checked and most likely refurbished (capacitors) which would not be worth the money.

Second, all of the speakers you've listed are were "college dorm specials"...about 20+ years ago! They're so old, plan on replacing the drivers. Again, not worth it

Third, what you have assembled may be good for "head-banger" rock and roll, but for the type of music that you like...forget about it.

You cannot assemble a decent mid-fi, let alone entry level hi-end system, with your "flea market" buying attitude. You can definitely get lucky, and occasionally find some great vintage equipment at garage sales or swap meets, but what you have doesn't qualify! Do some research, and read the posts at Agon regularly. Just because it's old doesn't make it "vintage".
I disagree (respectfully) with Fatparrot, in part, and I agree, again in part. I would say that the A70's and the Marantz qualify as vintage equipment and possibly the Missions as well. I think the SR2000 would drive the A70's quite effectively as they are an easy load. I still own a pair so I speak from experience. I also think they would do a good job with your musical preferences. As to whether they or the Missions could replace your Bose, I feel that is a matter of personal preference. I certainly feel the A70's are superior but it is really your opinion that matters.
Fatparrot is correct that your equipment may need some service. However this may not be all that expensive. I would recommend that you check out where you can get advice and information from a group who specialize in vintage equipment. Lots of Boston and Marantz fans there and good, helpful people too.
I'll also agree that SACD is probably not the way to go unless you plan on going to a multichannel system in the future. As long as you stay with 2-channel systems you really won't be able to take advantage of the SACD format.
Anyway I hope you enjoy your equipment. I think you'll find it can give you a lot of musical satisfaction. Good luck.
Thanks for the help. I'm going to check out the A70's soon. Also, thanks for the referral to Audiokarma, it seems to be a good place to lurk around.

In defense of myself, the speakers and receiver had been checked out and repaired already at time of purchase. Second of all, as a college student living in a small dorm room, I'm not headed for a pair of Nautilus's and McIntosh gear any year soon. I'm Just trying to get the best I can for the most I can afford. A little advice in that direction certainly wouldn't hurt.
Alo, my apologies! I kind of hit the nail on the head with my college dorm room crack...I didn't realize that you were actually a struggling college student! Your taste in music threw me off. Kudos to you for your taste in music, and your attempt to get the most value for your dollar, and not just strapping on an MP-3 player with cheap-ass headphones! I also didn't realize that you had your gear checked out...many people don't even bother.

So, what are you using for a source? Is your system in a dorm or other small room? How loudly do you like to listen? What is your other receiver? How do you budget your you currently have any cash to burn now? Have you decided on speakers for your next purchase?

Again, my apologies
At home, we're running a Sony SACD player w/ a DA3ES driving the Bose 401's. At school, in the dorm room I'm running the Marantz/Mission combo and my source being an archaic JVC cd player and the headphone out of my Powerbook. Basically, I'm stuck with the Missions until me and my roommates move to a bigger house, so I was wondering if the A70's were worth the pickup and could possibly be used instead of the 401's at home.

As for budgeting my purchases, if it seems reasonable, I make it. Right now, my summer cash is running a little thin so I'm looking for really cheap stuff. Come end of summer, I might throw down for some B&W 601's (then agan they may not be worth it). I guess to go in the other direction, I'm trying to resist picking up a more modern 5 disc CD changer. I'm not really sure which of the slightly older models I should be interested in. Especially since all that seems to pop up is Technics, Sony and sometimes Pioneer (I'm not missing something am I?). If anyone has any hints or suggestions as to if any slightly older CD player is worth a pickup... I'm also looking to pick up a record player as another source, but that's another story...

Anyway, my mode of buying is to shop for items that people seem to have forgotten the value for or are trying to get rid of. I highly recommend this for anyone who likes picking up good finds or needs to spare some money.
FWIW i think what you're doing is great. right now i'm listening to a pair of modified/upgraded hartley bookshelf speakers that i bought at the local habitat for humanity resale store for $24. with upgraded tweeters and crossovers from hartley (plus a few enhancements of my own), they sound GREAT to my ears, especially with acoustic music and jazz in particular. they have a very clear midrange with great presence and detail, smooth yet fairly detailed high end. about $200 plus my labor in them total, and i'm pretty sure that i would have to spend about $1500 to top them (which is about how much my previous pair of speakers cost), given their strengths. i have at this point sold off nearly all of a previous ~12K system, and have almost all vintage equipment. i graduated from college in '89, earn 6 figures, and couldn't be happier with my stereo system. my main advice would be to stay off the audio merry-go-round/vortex of expenditure/resale/expenditure/resale, be happy with less, choose quality vintage equipment carefully AFTER having done your proverbial homework (no pun intended), and above all enjoy the music! you might want to look at some of the later entries in the "building high-end tables cheap" chat thread for some of jean's experience with/opinions of vintage equipment. the man knows his s#!t.
quick follow-up: using my "new" refurbished/modified vintage lenco l-75 turntable with high quality arm and cartridge (admittedly not vintage), feeding a vintage sony ta-e88 professional preamp (stellar phono stage) and 3130f amplifier (both with all original capacitors--for now) and the aforementioned speakers, with good quality modern cabling all around (IC between preamp and amp cost more than either). listening to the classic records reissue of the famous dylan '66 "royal albert hall" concert, and in the lead-up to "like a rolling stone" i could hear clearly FOR THE FIRST time dylan say to the band "play it fu@#ing loud!" i love this hobby! i think i'll buy a SACD player after all.