I'd have to say that even within the incredibly small niche market that is 1/6 scale movie replica figure collecting, collecting Predators is an incredibly smaller part of the niche.
I love HT figures(And making customs), plus i also love the Predator movies(Yes, even that lousy AVP, lol), but i'd not waste £10 on a Predator figure. It's purely a personal thing but, when you buy a niche within a niche product like Predator, the resale will be a lot lower than other figures.
Who would have thought that ScarJo from IM2 would be worth so much on the secondary market and Predators would be worth so little?
There are the "2-in-1 Superman" figures out there, and there are the "New Goblin" figures.
It's a gamble when you buy as to which one you are investing in...