Tough question, basicly if you do not race then most likely there is no need to upgrade cranks unless you just want to.

As for the teeth, if the new crankset has a larger big ring it will give you more top speed, this is only if you already top out your current chainring. If it has a larger small ring it will make climbing a little more difficult if you spend a lot of time in your small ring. If it is smaller it will allow you to spin faster on your climbs.

The crankset really is not one of the top things to upgrade if it is not broken. You would probably get more benefit out of upgrading tires than you would a crankset.