Our first encounter with
DVC was also via renting, which we did for our vacation last month. The whole rental procedure went flawlessly, and I can't say enough about how helpful and accommodating the member was we rented from. That being said, you are still depending on someone else to make and control your reservation, and if you have to cancel, you are likely out of luck.
I personally like being in control, so the thought of having my own points as opposed to depending on others was attractive to me.
In addition, I think there is a definite monetary advantage of buying over renting, assuming that the market rate for renting rises over time (as you would expect).
On the other hand, when you buy, you are locked in to using your points, year after year, whereas with renting, you have no long-term commitment.
Personally, when I crunched all the numbers, I decided that while there is indeed some cost-savings to be realized by buying into DVC, one of the biggest benefits to owning is simply giving yourself an "excuse" to go to WDW on a regular basis--which is fine with me.
