Coop, a bike that old of that level is worthy of some "tuning upgrades", so you might consider a quick makeover. Beyond that, upgrades aren't your best move on a "platform" that's limited by its nature. I'd suggest:
--new brake pads: Kool Stop dual compound, low profile
--new grips: update with something to give the bike a new feel.
--new tires: update with higher volume, and check out the WTB MutanoRaptor 2.4 for the front tire...killer for rigid bikes! Try a Velociraptor 2.1 or similar for the rear (narrow and aggro knobs).
--lube/clean or replace cables for derailleurs and brakes
--lube/clean or replace chain ** but don't replace it if the cogs are worn, just lube in this case**
--saddle: how old is that thing? Seats have come a long way since what came OEM on the 820.
--dial in those derailleurs, tune the wheels for true
With that, the old 820 should be better than it ever was and a load of fun to ride. Something to get your appetite whetted for a later upgrade and then a loaner bike you'll be proud to use to lure new victims with.
If you really want to upgrade more, there's one thing I do on rebuilds of old bikes for buddies: Avid 7 levers and brakes. They're the most bang-for-the-buck system you can get in vee-brakes, are super easy to tune, are lighter than what you'll trade them for and work great. You can find them online in combo-pack deals for levers and brakes together. Still get the Kool Stop combo pads if you do this, btw.