i leave 4 separate clients open and i don't even mine. i do it for philosophical reasons to "help" the network. doesn't cost me anything.
Everything costs something!
If bitcoin becomes fully fledged monetary system things like enthusiasm, altruism, philanthropy and philosophy will not be enough to secure its future! After all, it is about money! All tricks will be used both technically and economically to game the system and abuse it. Every expense that is possible to avoid paying will not be paid by participating agents in the network! There is no doubt about that... The big question here is whether all those avoidable expenses are fundamental incentives to keep bicoin network running?
I think this is the most important point. As a concept for a community, bitcoin has been better at making miners than at evangelists and transaction processors. I see this as a game that has made winners out of miners, but is missing players, now. This is a shortcoming of the system of incentives.
Miners are transaction processors. Mining is how they are verified.