Umm... that's exactly one of the issues that we're cargo-culting about the most. There are two general categories of solutions to this problem: technical increments (ie. a better constant factor), and fundamental cryptographic upgrades (eg. the stacktrace challenge-response concept we have been talking about on our blog). The first category we are not yet doing because we are following the well established advice of "don't prematurely optimize". The second category, well, that's why we're thinking of ideas like distributed blockchain storage, clever algorithms to force more people to be full nodes, and challenge-response protocols. There is also another idea I was thinking of, which I'll have a post up over the next week or two.
In the long term, we are already beginning the development of a very widespread collaboration with academic groups to try to tackle the problems in cryptocurrency, and at this point we fully expect we'll end up releasing Ethereum 2 at some point in 2016 which would take a lot of new cryptography into account.
