ideally within 1500 miles of upstate NY
If you said, "the West Coast" instead of upstate NY, then I know a great fit. I'll have to defer to others -- I only know one timeshare system inside and out. It does what I want so I've never had to learn the others.
But I would definitely be open to other options besides "buy more RCI points." If you ask how to buy more, that's the answer you're going to get. If you ask "How do I take several vacations in the Northeast on one maintenance fee," you'll surely get more interesting answers.
There was a recent post by someone who owns a week in upstate Maine. He's getting two exchange weeks a year (plus the ability to score dirt-cheap bonus weeks) on a maintenance fee of around $400. Probably the best example of "timeshare math," I've ever seen.
There are many paths to the same mountaintop. Timeshare salespeople never mention this. They only talk about THEIR path to the mountaintop. That's their job. And in general, timeshare owners also only talk about whatever it is they happen to own. So you have to throw out a very wide net -- "I want to do this. Can it be done?" Google is useless because the top results are all paid advertising.