The main reason people would want to mine at your pool instead of straight on P2Pool. Is massively reduced variance on merged-mining. Otherwise they would have to solo merge-mine the alt-chains. Which unless you have about 30Thps is pointless.
Good point, the alts would be pooled whereas the aren't if solo p2pool mining.
For those asking about the pool being down, the front end website was being spammed/scraped by a bot causing issues there. I've banned it for now as it seems to have gone crazy. The backend mining was still accepting and processing shares.