We are doing this, sort of. We really only intend for now to go once a year, in a one-bedroom, and will probably never stay on weekends. However, the relatives we visit on the weekends are elderly, and we're not sure how many more years we will be visiting them. Also, our kids are little and a one-bedroom is perfect for now, but I'm sure a two-bedroom will be really nice when they're bigger. So we bought enough to cover future vacations when we'll need more points so we don't have to hassle with buying it all again, and we're planning to rent out the extra now.
Of course, we have the best of both worlds in that somehow we know lots of people who are dying to rent points, and are thrilled to rent from someone they know (and we are thrilled to rent to someone we know as well - obviously we'll have to make sure that everything is clear before we do so, but anyway...), so finding renters we trust won't be a big issue. I just thought we'd rather have enough points that we could do what we wanted to in the future, and rent when we didn't need them.
And it's paying off this year, since we've decided to take the whole family at once and got a GV - something we could not have splurged on if we hadn't bought the extra now.