I have no doubt that transaction fees need to increase over the coming years but if all miners exclude transactions now (if one's doing it, then why no all?) you'll be sitting in your sandbox alone pretty soon without kids to play with. So play nice.
Really? If it cost 0.01 BTC (roughly 5 pennies) to send any amount of money, anonymously, securely, and safely anywhere in the world there would be no value to Bitcoin? If you think that Bitcoin can't survive with fees 1/100th of Paypal or VISA what are you doing here? Personally I think Bitcoin is valuable even with higher fees but I am willing to start at 0.01 BTC. I won't be "playing nice". Playing nice has simply led us to this point where people think refusing to include transactions (THE RIGHT OF MINERS) is an exploit. Miners can't make the network pay a fees but they certainly have the right to exclude transactions.
Any fee that's considered reasonable or unreasonable by looking at the current exchange with US$ is introducing a factor of indexation with the dollar.
IMO the fee should be adjusted, like difficulty, in terms of the previous blocks, so that they are expected to add up to a certain quantity per block.
Let's take, for instance 1000 blocks as the unit of adjustment (1 week is 1008, so 1000 blocks would roughly include the variation expected during weekends/workdays and low/high hours) and let's say we want the total pay-out coming from fees to add up to 60 - current_block_reward (making total reward from fees + block discovery more or less stable at 60 over time). With 100 average transactions per block, that would mean an average 0.1 fee right now (60 - current_block_reward = 10). With 1000 transactions, that would mean a 0.01 fee. We'd need more transactions for this to be viable, and we'd need many more as block reward decreases.
Note that any mechanism forcing people to pay a fee will most certainly lead to fewer transactions. Users would try to bundle more payments in fewer transactions. Obviously this also leads to less blockchain bloat, but as a general rule I think it's safe to say we want more transactions.
The voluntary fee scheme is something I saw as a potential source of problems since I first read about it. As you say, miners can't make the network pay a fee but they have the right to exclude transactions. This can lead to an uncertainty over what fee will make my transaction go through that ultimately hurts the whole system. I believe we will have to abandon this charity shop style of operation and switch to a "serious business" style of operation, where people know expected prices and are given some guarantees of getting what they paid for, in regards to fees and transactions.
