The issue of buying resale vs from the developer doesn't really factor into it. If you want more points, you have two choices:
1. Buy another week. In most cases (except for a few affiliates), the points will go into the same account, as long as you purchase under the same name(s). You'll pay only one club fee per year, but you'll pay two maintenance fees.
2. Sell what you've got and buy a week with more points. You'll have just one MF per year, but it may be higher if you've bought a larger unit.
Now, buying from the developer could facilitate the 2nd method. That is, they'll make it painless to simply upgrade to a larger unit, taking the smaller one as partial payment. So in that sense, a developer purchase is easier. If you go resale, you'll have to do the sale and purchase on your own. But really, the two options are the same whether it's resale or developer. But the resale method will be much, much cheaper.
-Bob