We bought 250 points over a year ago and find that to be a great number. IF we could afford more, we'd have bought more. We went for New Year's Eve adn got a great two bedroom at Saratoga Springs (our home resort). With the high demand night of New Year's Eve we were able to stay 4 more nights at cheap time (pus had 20 left over). What I think you should consider is how many bedrooms you would want, when you'd want to go and if you think your kids will want to take friends.
you can bank all of your points from one year and borrow from teh following year. So, if you have 250 points you can actually use 750 at one time (3 years worth) and could even go on a cruise. We are going to florida for a wedding in two weeks adn found it much cheaper to fly into orlando than fort meyers (on southwest) and decided to use a few points for 3 nights and use our annual pass we bought. All we are paying for is a rental car (@ $100 wk - bargain) and miscellaneous food, souveniers etc. It gives us the flexibility as a couple and family now and in the future. Plus, I have older stepkids - what better gift than to give them a vacation with their families one day. I just wish we had more points - I want to go on the Safari after the kids grow up! When we are old and grey, my husband and I will be able to go to Florida for a month (in the off season) and not have to worry about maintaining a yard, a pool etc, with the exception of annual dues - which at Saratoga Springs were only about $700 this year - cheapest of all resorts. I hope this helps.
Anne