Transaction spam is not a high-priority issue, in my humble opinion, and I don't think we need to do anything more right now.
We were running into big free-transaction backlogs because of the rise in popularity of the mining pools, but with the big pools now using the new sendmany feature to pay (with a transaction fee) their users that issue has gone away.
The improved -limitfreerelay and sendmany will both be in the next release, which should further improve the situation. And I think in the next few months lightweight download-headers-only clients will start to appear.
I would much rather see work on optimizing the network protocol so that hashed of already-spent transactions deep in the block chain aren't sent to (or stored on) new nodes joining the network.