Maybe I'm getting old, or maybe I just found where I'm comfortable, but I doubt I'll purchase 4e.
Maybe, BIG maybe I'll buy just the core books, I but I doubt that, too.
Currently I play in a Arcana Evolved campaign, for which we have most everything (more than we need sometimes), and we're geared up for an eventual Ptolus campaign once we hit 20+ levels in the AE/AU campaign.
I've got two sets of 3.5, for the rare instance when someone doesn't have the books, and I've downloaded SRDs, including the one I bought from CMG (nicely referenced PDF library that works wonders for the rare moments my lazy butt actually acts disciplined enough to put put a submission).
I don't really need 4e and, personally, I think it's way too soon, as a customer, for it to exist - however, it's not the customer that makes this call, it's the company, so who knows.
Honestly, if I were to do a new system and stuff with a 4th in it's title, I'm more prone to really push myself into the GURPS Fourth Edition books I've sitting on my shelves. I liked it enough to buy them, when they first hit, even though I've not played in a GURPS campaign for years.
Anyhow, that's just my two cents explaining my "Maybe the core books" vote.