Replace my B&W 802's?

I have an old pair of B&W 802 series 80's. These speakers were bought around 1987 and were produced before B&W made the matrix speakers.
I love the imaging and detail of these speakers but if there is one weak point, it's the bass. There just isn't much punch on the bottom end. Do I consider adding a subwoofer or is it time to move on from the B&W's? My budget for a subwoofer would be about $750-1000 for a used one. In addition, if the sub is not going to be worthwhile what are my B&W's worth and what kind of speakers might I consider?

What electronics are you using? To me your situation is perfect for a sub since you love everything else about the speaker.

I suggest inserting a crossover between your preamp and amp that creates both a summed mono signal for a sub and left & right high-passed signals for the 802s. The NHT X2 will do this, but won't leave much budget for the sub. Hsu Rsearch has a high-pass filter only for 1/3 the price of the full featured X2. Some subs like many from Velodyne have builtin high-pass filters (typically first order).

I would suggest the largest box with the largest (no smaller than 12") driver you can afford.
Subs don't add "punch" to the bottom end. I would say new speaker time and/or an amp with more bottom end definition.
You may want to considering the B&W Matrix line 801/3 or 802/3..Since you already like the B&W sound..You won't have any lack of bass... with either of these.........
Subs don't add "punch" to the bottom end.

LOL! Too funny.

The fundamental problem with floorstanding speakers is that you can't place the bass drivers where they need to be without dragging the mid/treble drivers along thus losing the optimal location for imaging. Subs offer a perfect solution to this dilemma.
the matrix-802-s3 is one of the best speakers B&W has ever produced. placed on some sound-anchors, with a maughn box (bass alignment filter), you can (almost) forget about what else is out there (almost) forever. i want to use the word "perfect" to describe their sound- open, dynamic, fast and deep bass, revealing, resolving, etc. the kevlar midrange was/is a difficult driver to beat (they still use it, but have modified the surround). it has some (relatively minor) faults, but you'll be enjoying your favorite music way too much to be thinking about those.
I'd get a later model Matrix and update it with a Northcreek Xover or the Golden Flutes from JPS. Don't forget the Sound Anchor stands.
french fries
Can you elaborate on the sound anchors and the maughn box with your 802D's? What is the maughn box exactly and which stands? Splain your setup please...
i personally had the 801s3's with sound anchors/tip toes and a maughn box. sound anchor makes an excellent stand and mechanically grounds the speaker which tighten's up the bass.
without good stands or at least the manufacturer's supplied spikes the bass will be poorly defined and boomy. the maughn box is no longer made; krell also used to make an aftermarket bass alignment filter (fancy name for an equalizer which boosts the low bass frequencies by a few dB's). although there is an audible difference between inserting a B.A.F. between the preamp and the amplifiers (requiring extra interconnects)
it is not a necessity- that is, unless you have a large collection of pipe organ music.
older B&W 801's and 802's included a stock BAF- a small black box that usually just fit behind your rack on the floor. it didn't look like much so krell and Maughn, inc.
decided to make a more sophisticated unit (for about $1000).
the maughn box mimicked the levinson 23/27 amps-black anodized face with a red led, so it looked very nice (as did the krell). the sonic improvement over the stock filter was pretty subtle, at least with the audioquest wire i had at the time. my pitch for the 802's is that i heard a pair play a bruckner symphony- they sounded really great, with very deep and nimble bass. OTOH, bass down to 19Hz in a relatively small speaker system made the 801 fairly unique at the time, although the 12in. woofer starts and stops a bit slower. read lipnik's review of the 801 if stereophile still has it on their web site, or the 802 review in the absolute sound. they will go into more detail than i can go into here about the speakers' designs. i still get a kick out of lipnik's parting comment that the 801 was "the audio end of the road"- i.e.- at the time, one of the best speakers you could buy at any price.