There's actually a lot of value in the role of a concept designer/whatever-it-is-you-labelled-yourself-up-there. To be honest, I'd value a great designer much more than an excellent artist. There's a lot of artists around Brilliant designers are gold.
Also mapping is quite a specialised skill if you can do it well, hell, I've had these games since they came out and never really figured out how to texture nicely in WB
The problem is that as modding is a voluntary type thing, it's all very ego based - so unless you can prove to other talented people that your mod is worth your time, you're not going to get so far. That's not to say your idea is bad. You just need to prove to all the grumpy old men that you're worth it
Don't give up, but just take a measured approach to the big ideas.
+ Take the encouraging things that all these other folk have said