A guarded "no."
As others have noted, I get far more bang for my buck from Pyramid. Now, throwing the resources behind Dragon and Dungeon magazines definitely adds oomph to DDI, but I don't buy those anyways, and generally only read the Class Acts and cartoons in back and Greyhawk-related stuff. (I hate the Forgotten Realms fluff. Anything from Ed Greenwood is expensive litter box liner. Eberron is conceptually cool, but has never enticed me. I keep thinking that the setting creators keep thinking how cool it is, so it comes off as a kid who tells everyone loudly at every chance he gets just how cool he is. And I don't need more monsters or another cap system.) Still, we're talking about about a tested, developed adventure every couple of weeks, maybe something like the Adventure Paths. Since the expenditure is just $10 a month, I can see this if I bought fewer books.
What I'd prefer is buying are the core books then the DDI and then nothing else. Make additional printed product rare things, often compilations of DDI or really ambitious topics, like psionics. Make the Complete and Races series (the former is about the only additional printed material that interests me anyways) online things, a prestige class for arcane, divine and martial characters each a month, along with a constant, slow-but-steady diet of new feats, spells, monsters and magic items. For new crunchy bits, you rarely need the whole book at the table, so a printout is preferable. Wizards would get a bit more of my loot each year and spend less money on printing and shipping.
Oh, and the lack of Mac support doesn't help me pull out my credit card, though I expect that to change after the first year or so.