Thing is, in such an unlikely event, bitcoin would change to SHA-512 or whatever would be cool then, overnight. Altcoins could serve some purpose I guess, as experimenting grounds with various chain logic parameters, or lighter coins for some lighter purposes, but I think it's a pretty solid statement that none of them would match BTC in value without some very serious investment / backing first. Any good advances in altcoins could be easily ported to bitcoin, with it's brand name recognition and infrastructure, so just "being better" in something minor won't do it.