I agree with the OP that if you have a good, strong, cost-effective alternative to wood, then absolutely go for it. If you're planning on keeping the boat for a long time, you'll NEVER have to deal with rotten stringers ever again. If you're selling it, then you don't have to worry about it in the very long term anyway. It will be solid for a period of time either way, and I think you're taking the right approach with a little testing first. I also think that the trex stuff would be a lot more agreeable to a patch, or filling a hole from a stripped bolt or something. With rotten wood, you have little chance of that. As long as you do what you're doing and test the bonding, it should be a great solution.
If I keep my boat for the long term (it's been 7 years actually!) and if I go through the massive effort of DIY floor and stringers, there's no way I'd put wood back in there unless the cost was overwhelmingly less. No foam either!
I have to rebuild my rear floor piece over the stuffing box and I'm thinking of going with aluminum, just so I never have to touch it, ever again...
1989 Bravura - repowered with 2001 PCM 351 GT-40 - 1.23:1 PCM Trans.
1989 comp - sold
1985 comp - sold