The more you plan to go, the more it makes sense to buy in. Disney vacations are probably not going to get any cheaper, you know what I mean?
Keep in mind, there are maintenance fees every month, and you'll need to factor that into your budget. I suspect some people buy a lot of points during an odd occasion when they have some sort of windfall of cash, only to not go as much as they thought they would, or start hurting on the maintenance.
The plan for my betrothed and I is not to go every single year, but to go 2 or three times in one year, then take a year or two off, go other places (Yes, there are actually "other places"

). When we can afford to do so, we may buy extra points to make sure we can always at least stay in a one bedroom. It is very convenient to pack less, throw a load of laundry in the wash in the morning, dry it when you get back to the room, and never have to hover over an open laundromat for fear some freak will steal your wife's bra! And the option of taking a night off, making a little dinner in the kitchen and veg out for a night is a nice option as well.
We would also probably opt for the discounted annual passes, which would then make sense for us to go two or three times in a one-year period. And if we run out of points, then we can use the AP discount for rooms at resorts that aren't part of the DVC, like the Animal Kingdom Lodge or even Port Orelans Riverside. It gives you affordable options.
Some people think of traditional time share as an investment, something they can sell if they need to. You won't make a profit selling DVC, but like I said earlier, if you know that you'd like to spend many vacations at WDW, it's not a bad way to plan ahead.
But if you're still not sure, consider this: Many DVC members rent their points if they know they can't go to WDW in a given length of time (OR, if they just need some quick cash). I think most people rent between 11 or 12 dollars a point. You can always rent some points and set up a vacation that way, see how you like the experience, maybe even do one of the DVC tours for more research...
For a one-week stay at Boardwalk Inn Villas, preferred view, if you rented the points necessary at $11 a point, a studio room would cost between 1144 for the week (value) and 1991 (premiere). To pay rack rates for that same room for 7 nights would cost between 1883 and 2723 (give or take, I'm using info from allearsnet.com and the DVC timeshare store, so my accuracy is partially based on theirs). So you'd save at least 700 dollars renting the points, you'd still get a Disney vacation out of it, and you'd have the opportunity to determine whether or not DVC is right for you.
As I sais, something to ponder...