Is it worth upgrading fr McIntosh MC402 to MC501?

I currently have a McIntosh MC-402 have a chance to upgrade to a pair of MC-501 mono blocks. I am wondering if the MC-501 is significantly better over the MC-402 considering it is about 50% more in cost in the used market. In other words, would one be able to tell the difference? I am using a C46 (C-46) preamp, B&W Nautilus 802 speakers, and an Oppo SACD player.
What speakers are you using, and what is their efficiency rating? That would make a difference.
IMO, as a 402 owner..with the speakers you have its not worth the extra scratch
I have had both the 402 and 501's with a C46

I would not go to the 501's unless you are having difficulty driving the speakers you have.

You would notice a slight difference, but imo, it would just be a "flavor" difference rather than feeling one amp is better than the other(s).

Actually my preference was for the 402, as i thought it sounded a tad "sweeter/smoother" than the 501's ....

my 2cents

If anything I would sell the 402 and buy a 452 if you want to upgrade. I think the newer power supplies in the 452 would provide a more noticeable improvement than the extra power. I have a 402 and would love to get the 452 but it doesn't fit my budget right now.
The 501's are special but not a significant step up sonically or financially - especially since you already have the 402. I auditioned both extensively before I purchased the 501's and they were both excellent, I was leaning towards mono's and that's what swung me.
IMO I disagree with Theo..the 452 sounds a little better depending on what your sustem is.. but when you figure your spending approx 4K+ after you sell your amp ,and agin the speakers you have as far as detail etc...not worth it
I would spend the cash on upgrade the CD instead. Esoteric or Wadia and upgrade the cables. Personally, I would get the Wadia because it has preamp build in.
The net difference between what I can buy the 501s for and the price I can sell my 402 for is about $2000 more.