3.5 books will only be "obsolete" if you're actually playing in a game that uses 4th edition rules. Hell, they're obsolete if you're playing in a 2nd or 1st edition game, too, and some people probably still do play 2nd edition.
People still play Planescape, Mystara, Dark Sun, Dragonlance, Spelljammer, and they've all been out of print for years. Though I [i:34jg4guh]have[/i:34jg4guh] seen a PDF of 3.5 Ed. Dragonlance, and Planescape has been reworked to fit 3.5 rules by a group of fans of the game, even sanctioned by WoTC to be an "unofficial official" release.
The point I am trying to make is, it's up to the group as a whole what version of the game they wish to play. If someone wants to play 4th edition, but the rest of the group don't, then they don't GET to play 4th edition, simple. No, you can't introduce game mechanics from one version into another. Not very well, anyway. 4th edition stuff will have to be "reverse engineered" to fit 3.5 edition rules, or 3.5 stuff can be tailored to fit 4th edition rules, but you can't mix 3.5 rules and 4th edition rules and have it "just work."
As for buying the books, if you don't have the money, don't buy them. You don't [i:34jg4guh]have[/i:34jg4guh] to have the absolute latest and greatest . I brought my 4 books (3.5 DMG, PHB, FRCS, and MM2) over a period of 2 years. Total cost was about $270. Okay, so you might need the books to play in that new campaign the DM is going to run next weekend. If that's the case, I'm sure others in the group would have some of the new books, and I'm equally sure they'd quite happy to let you check through them as needed.
Alternatley, you could just snub your nose at 4th edition and stick with 3.5 for a few more years. Change is good, change stimulates growth. I'm certainly glad we're not still stuck with the overly-complicated and algebra-like mechanics of 2nd edition, as rich and complex as the game system was, it was TOO complex. Bring on the changes! I for one can't wait, even if just to satisfy my intense curiosity.
Anyway, this is getting way off topic. If people want to discusss game mechanics and how they affect players, maybe be best to take this to another sub forum.
