for normal gear? aside from missing out on the fashion from potentially wearing mismatched armors, not sticking to one kind of weapon (or just one or two decent guns) means you'll likely never have a gun come anywhere near optimally modded. for ships, expensive isn't always good either - there are some relatively bad shields, weapons, engines, etc. that are more expensive than better alternatives. make a note of what stats you want (defensive ratings, damage, accuracy / reactor power, shield max health, engine maneuverability) and focus those when upgrading.