Sweet Tooth is worth switching to Magento for.
Altered Cart Cash Rewards (for X-Cart 4) has most of the features, but not all.
Disclosure: I have the AC cash rewards on my site, and have worked closely with Bill Brewer to make it a very important part of my customer experience.
Features that CR offers (and missing from most loyalty/points programs):
1. Reward accumulation rules. Earn rewards for various results or purchase. Rewards for specific products or categories. Rewards if a customer does an action (registers, posts a review, etc.)
2. Reward redemption is not tied to coupons or discounts or payment methods. Customer can apply rewards in checkout before any payment method, and does not require a round trip back to the cart to redeem. THIS IS one of the most significant UX features missing from other "points" modules.
In my opinion, a loyalty program must integrate at many levels, including registration and email lists and tell-a-friend and product reviews, etc...
If anyone wants to see my AC Cash Rewards integration, PM me.