So... I start from "more transactions == more success"
I strongly feel that we shouldn't aim for Bitcoin topping out as a "high power money" system that can process only 7 transactions per second.
I agree with Stephen Pair-- THAT would be a highly centralized system.
Oh, sure, mining might be decentralized. But who cares if you either have to be a gazillionaire to participate directly on the network as an ordinary transaction-creating customer, or have to have your transactions processed via some centralized, trusted, off-the-chain transaction processing service?
So, as I've said before: we're running up against the artificial 250K block size limit now, I would like to see what happens. There are lots of moving pieces here, so I don't think ANYBODY really knows what will happen (maybe miners will collectively decide to keep the block size low, so they get more fees. Maybe they will max it out to force out miners on slow networks. Maybe they will keep it small so their blocks relay through slow connections faster (maybe there will be a significant fraction of mining power listening for new blocks behind tor, but blasting out new blocks not via tor)).
I think we should put users first. What do users want? They want low transaction fees and fast confirmations. Lets design for that case, because THE USERS are who ultimately give Bitcoin value.