It seems to me having miners share 'near-miss' blocks with each other (and the rest of the world) does several good things.
As Greg say, that tells you how much hashing power is including your not-yet-confirmed transaction, which should let merchants reason better about the risk of their transactions being double-spent.
If the protocol is well-designed, sharing near-miss blocks should also make propagation of complete blocks almost instantaneous most of the time. All of the data in the block (except the nonce and the coinbase) is likely to have already been validated/propagated. See Greg's thoughts on efficient encoding of blocks: https://en.bitcoin.it/wiki/User:Gmaxwell/block_network_coding
So there could almost always be no advantage to working on a smaller block rather than a larger block (it would be very rare to find a full-difficulty block before finding-- say-- a 1/100'th difficulty block).
Near-instant block propagation if you 'show your work' should give un-selfish miners an advantage over miners who try any kind of block withholding attack. And it should make network convergence quicker in the case of block races; miners could estimate how much hashing power is working on each fork when there are two competing forks on the network, and rational miners will abandon what looks like a losing fork as soon as it looks statistically likely (based on the previous-block pointers for near-miss blocks they see) that they're on the losing fork.
We can do all of this without a hard fork. It could even be prototyped as an ultra-efficient "miner backbone network" separate from the existing p2p network-- in fact, I'm thinking it SHOULD be done first as a separate network...