I personaly don't like xtc's rating system very much.
My option would be a system similar than the one in cbc league, which is i think based on chess rating system (ELO). So is xtc, but with different starting points and rating changes.
The basics of my proposition are same as in xtc, but instead at 500, scheme rating would start at 1000. We'd keep the calculation for overall rating - simply adding together scheme ratings. Rating change for wins/loses would remain the same, 0-30 points (rounded to whole numbers, without decimals), with a little adjustment, for example so that high ranked player would win at least 2 or 3 points when winning against low ranked player.
A problem is, when a less skilled player plays a lot of games and loses most of them, his rating quickly drops very low (like 100 or 200 in xtc), which is imo a little discouraging, especialy for new players and playing against that player isn't rewarding anymore. That's why we'd set a lowest limit to which rating can drop (in cbc league ratings couldn't go lower than 1000 points). That way good players would easily go over 2000, less skilled wouldn't drop down to 0.
These are more or less cosmetic changes, but doesn't it feel better to have rating of 2500 than 800?

We'd have 2 ratings, one for season standings, which would be reseted after every season, and the overall rating, which would show player's performance over a longer period of time.
Would this way be unique enough?