I looked up all the remaining "sports" .pro domains last week and saw that Darts and Snooker were pretty much all that was left. I don't think either are going to become Olympic sports anytime soon but I guess they might be worth a small sum to an enthusiast, club, or niche retailer if the extension took off.
I don't understand why you registered Darts ahead of Snooker. Snooker tables cost £3,000 and dart boards cost £20 in Argos so from a retailing point of view Snooker wins hands down.
You play Darts in a pub or bar but Snooker is played in specialist clubs which could all be potential buyers for Snooker.pro so again, I would say there is more likelihood of being able to sell Snooker.pro.
From an online gameplay angle, I reckon Snooker edges Darts. You get Snooker games on the Playstation and Xbox but Darts is harder to do justice to. Presumably, once you know where to line up your cursor you're in treble twenty every time.
Snooker edges Darts on Google uniques but Darts whupps Snooker on Overture, 40,196 Vs 15,610, so Darts wins overall on that count.
Xmas.pro would be useful for selling Christmas decorations, turkeys, low price Christmas gifts on-line. Nobody searches for it though according to Overture, everybody types in Christmas.
The problem with all these second tier .pro keywords is they don't have much value until something happens to boost the .pro extension. I'd say $100-$200 to a reseller or fellow domainer and up to $750-$1,000 to an end user who has heard of the .pro extension. If you find one, please let them know that Snooker.pro is also for sale.
To anybody who is late to the table and wants to acquire a sport .pro TiddlyWinks.pro is still available.