Vala is certainly interesting, but it doesn't do everything C++ does, even ignoring the legacy stuff. I know it may not be stuff that you need but it is stuff I use a lot. For example, there is no true multiple inheritance in Vala. There's no pattern matching of generic classes, hence no metaprogramming. There's not complete static typing, which IMHO is a huge loss when trying to use a language for very large projects.
Vala is cool. I definitely see the value in it. But it isn't a replacement for C++.