I've actually not been buying equipment from vendors (with credits anyway). My gear and mods come from drops and commendations. Seems to do me fine. Also, I don't want to go to great lengths to get myself completely geared up with everything as good as possible, spending a ton of credits to do so, only to have to do the same thing in another couple of levels.
I have 100k credits at Lvl 28, and really the only things I spend them on are medpacs, stims, and crew skill missions xD
Although I will splurge if there's a good item that takes up a slot I don't already have something in. (Like when I bought relics from the LS vendor)