There's one point I haven't seen mentioned yet and that is availability of goods, components or ships within the game being locked behind a kind of rep grind or other wall you can't just get passed with cold hard cash. It could very well be that having money doesn't immediately give you access to the "best" ships or components. It might be you still need to find that vendor somewhere, gain his/his factions trust through completing a series of missions and then be allowed to purchase.
A UEC sale may then just be a minor convenience... something you use because you lack that little bit of cash to repair or restock your ship, pay that NPC's salary or get that extra piece of hangar flair