I just downloaded the ixcoin client out of sheer curiosity... without reading about what it was.
My impression after mining for less than a day is that it is a bitcoin simulator. It simulates what it would have been like to be a bitcoin early adoptor, mining 40+ coins in less than a 24 hour period.
Only downside is there's no payout system! But, it's there if you feel like day dreaming and wishing you could turn back time.
I do think it makes for a great test net, and to have seen and learned more about bitcoin that I had missed with the main client. Not sure what you mean by no payout system though? I made a lot more BTC mining IXC and selling them then I usually do from a month a mining btc directly already.