Available slots only works for just so long, and then you MUST adjust it.  Minimal fees are fine as long as the network continues to grow and flourish.  If you are collecting 0.2 - 0.5 BTC per block in fees right now that is GREAT!!!  Because if the network increases 100fold that could rise to 20 - 50 BTC per block.  I know there are other factors to consider, but I am hoping that in 16 - 20 years (yes I'm not looking at tomorrow or next year or two) Our reward for solving a block will be higher than the 50 BTC we started with.