We've been growing our ownership over time through small contracts as well.
Did an original purchase of 75 points at BLT in 2010. Added 50 more through resale in 2011. Now, just sent off the deposit check for another 50 that will hopefully be ours in 60 days or less.
We seem to like to grow into our resorts. Originally we thought 75 would allow a studio stay every other year at BLT. Now, we're finding we'd rather either have a 1BR or be able to take friends and family and the 175 is better for getting a 2BR in certain seasons every other year.
Not sure where I want to be at BLT, but probably in that 200-275 range. Hard to say. We never thought we'd buy outside of BWV before BLT. Maybe we'll call it quits at BLT and buy when it's the Poly or the cruise line (making that up, but it sounds cool).
I wouldn't mind having more points than we need every year and renting out the excess to offset our dues. In years we want a big family trip - we have the points and in years we don't, we can subsidize the cost.
But, I don't think I'd ever want a contract bigger than 50-75 points. The flexability is just too nice in smaller contracts.