subaru impreza sport 2004 with 31000 miles...a little early for a new water pump and timing belts?

Yes because of the age of the vehicle. You never want to chance a timing belt, and when changing the timing belt, it needs to be off when changing the water pump. So why do it twice?

NO!...or at least not without inspecting the belt, which is easy to do. But if you change the belt leave the water pump alone, as they NEVER EVER FAIL! I suggest that my clients inspect their t-belts annually after the 12th year, but the lack of use of yours suggests you won't need one unless a tensioner or pulley gets loose. Changing t-belts used to be a $300-400 job (three hours), but wrenches are now trying to goose these simple jobs to $800-1k. Don't fall for it, as it's VERY expensive insurance against a very small failure rate. So I'm going to disagree with Rowefast's conservative suggestion on this one. At 150k and 12 years I'd be more careful....

I would say it is not reasonable but if you want to extend the life of your engine and you have the money to spend then why not?