Wow, not an easy question to simply say bigger is better. Room size is important - perhaps the 804's are just right for your room, but the 802's would overwhelm it with bass. Consider amplification (B&W's need lots of quality power); what you have now may be perfect for the 804's, and to get the same quality (not better) from the 802's you may have to invest a small fortune. Also, consider how important the lower octave is in your musical tastes - it may be important to you; it may not be. If not, why upgrade. Also, consider how far in to the room you can afford to put your speakers - the 802's may need a few more feet away from the front wall so they are not boomy. If it were me, I would not buy 802's unless I had enough room size and the proper amplification for them, and if I did not, I would only upgrade if I was willing to shell out the additional cash for the more powerful amplifiers. Also, I would say that if you feel you need the bigger speakers for more bass, you may save a lot of trouble, money, and get better sound overall by getting a good subwoofer. If you are solely interested in the midrange improvements that perhaps the 802's -may- have over the 804's (given the isolated enclosure) and have the proper amplification, then the upgrade may be a good choice. And lastly, in favor of your choice, the 802 does have a much heavier enclosure, which in and of itself (all other things equal) can perhaps provide better sound than the 804.
