1. Quantum computing is the most powerful model of computation we have based on currently known physics---in the sense that anything more powerful would need to be based on new physics. From the standpoint of theoretical computer science, a biological computer is "just" a different way to implement classical computation, typically with very slow speed but very enormous parallelism. It might someday have practical advantages, but unless we're totally mistaken about biology, it's not going to solve any problems efficiently that are outside BPP (i.e., classical probabilistic polynomial time). For that you need a quantum computer.

2. Yes, if quantum computing is successful, I imagine that might be good for the careers of many of the people involved in quantum computing.

3. Regarding D-Wave, there's this weird tendency to get fixated on words and definitions (but is it "really" QC or "really" analog?) even after you've explained the reality of the situation. See https://news.ycombinator.com/item?id=17426023 for my current summary.

Again, I'm skeptical that analog computers will ever be able to solve any problems outside BPP---for that I think you need a QC. (I.e., if not for quantum mechanics, I would have believed in the Extended Church-Turing Thesis. :-) ) Whether analog computers will ever again compete with digital ones on the constant factors, leaving aside the asymptotics, for problems that people actually care about, is a harder and more complicated question to which I don't know the answer.