FF1 is the new Hulk 1.
We can only hope.
Historically, this was the most valuable Marvel book.
I would really like to see it regain that position, although it is probably unlikely that it will ever pass up AF15.
Not likely that FF1 will catch Hulk 1. Its a simple matter of supply and demand. Currently there is less supply of the Hulk 1 book available. According to CGC Hulk 1 has a total of 1154 books graded, versus 1538 for FF1. That's ~30% less graded Hulk 1s on the market. That effects pricing a lot. That said, I do agree that the demand for FF1 will likely continue to rise, but so will Hulk - given he's likely the most stable character in the Marvel universe, since he doesn't age (thank you CGI). Not sure FF1 demand will rise at a faster rate than Hulk 1. Time will tell.
Fortunately, I'm a proud holder of both #1s and hope for nothing but a meteoric rise on both books!