If you are going to contribute to a Linux Desktop Environment, you are not the target audience for Elementary.
Elementary wants to be “the Apple of Linux”, to attract less-technical users and switchers from other OSes. Their development philosophy is similarly top-down: someone sets a “vision” and a small group of people gets to implement it. If you are a coder and you value bottom-up development, you should really look elsewhere.
Yep, that page is perfectly ordered by priority: funding, free labour for annoying tasks, and only towards the end, if you really really have to, you can give us a hand under the hood or even (dead last! Why are you still here?!?) help with design.
Vala is probably the easiest way to work with Gtk+ anyway, so might as well be Vala if the stack is Gtk. I don't know Vala well, but wouldn't mind jumping in with it, scares me a lot less than Gtk in C.
Be that as it may, it was a mistake to roll a different language for this in the first place. It's not really useful for anything else, so unless you're totally dying to contribute to GNOME (very few people do), there's no reason whatsoever to learn it.
Vala is about as easy to learn as any language could ever be. If you have experience with Java, C++, C# or D you can probably already read 97% of Vala code. And if it’s your first statically typed language, it’s one of the simplest.
Plus, most people don’t know most languages, so no matter what you choose, most devs have a language barrier. Vala, again, is very easy to pick up — certainly easier than C or C++ and probably easier than Java/C#/D.