Could resources be used for productive work instead, for example distributed computation? I'm thinking something similar to SETI@home, but with currency rewards for work done.
Perhaps this would also require a central issuer.
You can dislike cryptocurrencies for all sorts of other reasons, but that fact that some resources are consumed to keep it running really is going to be a feature of any sort of monetary system.
Of course, with physical attack there is always an arms race, but bitcoin is still vulnerable to physical attack.
As you suggest, one thing you could do to tackle the latter problem is to have a centralised entity to verify work. This could be implemented in existing systems by making the "work" signing data with the issuer's private key, and having the real work be negotiated out-of-band. This mechanism could be extended allow multiple independent issuers.
[0]: http://www.righto.com/2014/02/bitcoins-hard-way-using-raw-bi...
What people are asking is whether it's possible to adapt some kind of meaningful computation to serve the same function.
Instead of requiring a lot of computation, it requires a lot of waiting due to latency of random memory access.