My concern about bitcoin winding up more expensive is that it's a bit of a red queen's race. Unlike most applications of encryption, attackers and defenders are on even footing (except, like in most human spheres, in that defenders hopefully outnumber any coordinated group of attackers). This means that whatever latest best tech we have for efficiently turning power into hashes, we've still got to burn about the same amount of power to keep things secure (and continually update to the next newest tech). In other spheres, technological process makes doing the same work cheaper - but in bitcoin it stays the same; you've got to run as fast as you can just to stay in the same place.
It may well still be worthwhile, though.