ANYTHING can be sent to a mastering house, but you have to ask yourself if the recordings merit it, and also what your intention is for the mastered recordings (for sale? family? friends?)
Add polish to a mediocre recording and you get a polished mediocre recording... on the other hand, if the recordings are reasonably well-balanced and well-mixed, mastering can really make 'em shine!
It is ultimately up to you to decide whether the costs are worth it.... be brutally honest with yourself and then decide....
Bruce