Yeah, I mean, there are really two kinds of collectors:
You have the people who buy for nostalgia. These are the people who prefer the 1970s Star Wars Toys and the original Castle Grayskull.
Then you have the people who want the new and ultra-cool thing. This line will continue to have nostalgia, but it will at some point cease to be the new and cool thing.
He-Man figures will not magically go up and up in value forever. There's a bubble right now caused by an unexpected new wave of fans unable to buy the core characters easily. I'm not saying that Fisto won't still be worth money in 10 years, but not $100.
At some point, a wave of people will fall out of love with the figures and want to cash in. They'll want to display something newer and see how much money they can get. Then prices will crash.