1. I'm not sure why demurrage should matter unless you plan to hold the FRC for a long period of time.
2. I agree with you on PPC but not BTC.  Bitcoin blocks are found by P2pool fairly regularly and any shares you submit will be paid on a proportional basis whenever a block si found (p2pool finds blocks whether the multiport is on BTC or not)  PPcoin difficulty seems to have skyrocketed recently and I'm not sure why as it's been mostly unprofitable to mine, but it should definitely help a lot when we get more hashrate.

I am looking at other new coins to add to the multiport but I will likely avoid coins with too low difficulty (like ZET and UNO currently) unless they have difficulty adjustment algorithms that are more favorable to multimining.