I have almost 4,000,000 currently (I've used about a million over the years), and I plan to use them for travel when I retire. However, a case can be made that the longer you hold them, the less they are worth. I have several MVCI timeshares and my plan is to use my points to get me there when my income wouldn't support that.
I agree--the continued value of these points is in their use: the corporation could decide they are a liability and discontinue the program (especially if another lodging chain made the first move). The fine print says they need to give 6 months notice before elimination of the program. I too have used nearly a million of my points and enjoyed the time spent not spending money as I did.
The thing is, as a saver, it's hard to use 'em all up. I like the idea of using 150,000 or so each year to take a trip that may not have been so easy without the benefit of the points. Giving some away ...always nice.