In the not so distant future when the miners reward consists mainly of transaction fees, what is the incentive of a miner to forward received transactions to other miners?
To clarify, imagine you are a big miner (maybe a pool operator) and a transaction comes in from another node with a (considerable) fee. If you do not forward this transaction to the nodes you are connected to, you will reduce, admittedly by just a tiny amount, the chance that some other miner will include this transaction in the next block and reap those rewards if they find the block before you. By keeping it to yourself you can include the transaction in the next block that you will find.
If only one miner does this, the effects will be barely noticeable given the interconnectedness of the bitcoin nework, but if many miners have this behavior, could this potentially be a problem?

I am trying to figure out the size of the bitcoin economy and I have 2 questions for the bitcoin analyzers:

1) Does anybody have any idea how many bitcoins are actually used to buy products and services rather than buying other currencies? Any close approximation of that would provide a good insight of the utility of bitcoin. Perhaps this could help in understanding whether the recent peak is a bubble or not.

2) Has anybody analyzed the bitcoin transaction chain to see what percentage of the existing bitcoins are actually involved in transactions after their creation? Or, in other words, can one see how many bitcoins are actively participating in the bitcoin economy? Perhaps it is possible to see the percentage of not exchanged bitcoins in the last x months or days.