You are right. To summarise your answer:
1. quantum computers(qc) will be able to get you privkey from public key. But your address isn't your public key its hash160(pubkey). Do we need to change something with addresses after qc? Yes. When you spend money you reveal your pubkey(so every one could hash160 it compare with addr in the transactions and check that you have privkey). So 1) you should never send coins to the address from which you already sent something(its good advice to use new addr each time), 2) when qc will come bitcoin probably will make hardfork and will change sign algo.
2. About mining. There is Grover's algorithm which allow to speed up brute forcing of the sha256(this is what all miners do) but its not a inverse function of sha256. So we just get next mining revolution like cpu->gpu, gpu->asic and so on
I rarely say things without being mostly certain of them being correct (I do make mistakes of course). Most replies to this thread will just be useless, and a different/shorter version of what someone else said (i.e. legit spam).
Anyhow I'm not sure that Grover's algorithm could be extended to brute force SHA256. Isn't it supposed to be some sort of database searching algorithm?