OK i think i understand whats happened here, the payout is not going to my wallet address, that would explain why it tailed off after the version update gradually to low hash rate and then dissapeared from the stats page.
So does P2Pool take the wallet address from guiminer username field.
your problem is based on a to low hashrate i think.
p2pool s on a much higher difficulty. It takes about 40-50 min. to get a share with my ~830 MH/s. So, with your hashrate it will take about 10 hours or something.
without a share, you get no payout. And when you get a share early in one round, it could be that you also get no (or very low) payout, because it's pplns.
with low hashrates you should try a pps based node to p2pool, instead of running your own one, imho.