Hey guys, many thanks again to all for weighing in. I tried to reply yesterday, but apparently there's a 24hr/5-post limit here (presumably only for newbs?).
Anyway, all the points were tell taken, but some of them seemed have missed mine. I have no illusions about turning this relatively humble (originally $600) bike into a premium racer. But I like the frame, it hasn't been thrashed on, and I'm just looking to do some normal preventative maintenance, to keep this frame running for a while.
I'm definitely not intending to put lipstick on the proverbial pig, stupidly adding a bunch of expensive ultra-light race-grade parts. This is a 2006 bike, that came with full Deore componentry, mostly Bontrager stuff, and Avid disc brakes, so while it obviously isn't a "nice" bike, it ain't junk, either.
A new cassette and chain is a no-brainer. I've had some glitches with the main shifter, and the internet-suggested remedy of flooding it with WD40 then some Tri-flo fixed it quick, and for a good while, but I think it's time for a new one, and at only $28 delivered for a brand new Deore shifter, I think that's a no-brainer as well.
The Bontrager/Deore wheelset is original, and I cleaned/regreased the front hub a couple weeks ago, and there was some noticeable gouging on the cones, so that wheel probably isn't long for this world.
I broke/replaced some spokes on the orginal rear (back when i weighed an embarrassing 255!!), and since replaced it entirely. So I figured I'd just get a new matching wheelest, suited to my current riding habits, and (still relatively heavy) current weight of 200. I have bicyclewheelwarehouse sending me a set of all-black Sun Rhyno-Lites, with XT hubs, and DT spokes, for $145, delivered. That's a solid wheelset, that's gonna be pretty tough to beat for my needs.
Also, though it was hardly necessary, I ordered a new set of Avid brake levers, for all of $15 delivered (right afterward they changed their ad to include $6 shipping, so I got a great deal). The levers on it are the most worn-out looking thing on the bike, and I was just tired of looking at them.
That's about it. For a little over $200, I'm fixing up the drive train, and putting a rock-solid set of wheels on it, and it should be a great ride for a bunch more years.

P.S. as ironfish recommended, I'd already considered a rigid fork, but I like have a little front suspension for those occasions I might wanna scoot down a dirt road, and I'm not worried about the added weight. Also that's a big chunk of extra change added in to this project. If these low-end Rockshox crap the bed someday, I'll play it by ear at that point.
Also, as to the post about putting money into a lowly 26" bike, that will have no resale value, I'm not trying to increase it's monetary value, just it's functional value, to me personally. Also, I actually like 26" wheels just fine, largely because they are so common and cheap. As i mentioned above, I already have a stash of 1.75" street tires, that have proven to be fantastic tires, and only cost around $15 each. So I''m set for tires, for years !
Thanks again........