When all bitcoins are mined, then the big miners will probably move out of the market (if the transaction fees won't be large enough).
If big GPU/clusters miners move out, then difficulty will drop so much, that you willl be able to generate blocks easily using a single multicore CPU.


Not necessarily. If they won't be paying, and big miners exit market, then it will be very easy to generate blocks.
I think the market will self-balance automatically, and determine the best transaction fee.

As for I understand, BTC market value should be proportional to the work involved in getting more bitcoins mined (per block difficulty).
So, per-block rewards will stay always balanced.

And if there is high demand coin prices will rise and competition will drive up mining difficulty. The price of bitcoins determines the mining difficulty, not the other way round.

I presume that transaction fees will be rewarded in greater amounts to people who contribute greater processing power?

but will it still be profitable all the way up to that mark?  Or will the miners drop out much sooner than that?

Ah ok, I didn't realize that is how it works.  I thought the difficulty didn't drop.