In all reality, I never really found vendors much use. Out of the 50,000 some odd caps I've collected I've spent around 10,000, mostly on shipment supplies. .Legendary items seemed cool but they aren't that special or unique. Legendary enemies fall from the sky even on normal play, so you collect plenty of legendary equipment. Normally I would use vendors for selling stuff I don't need but that happens so rarely because I store stuff away with the intention of selling it but then don't get around to selling it because I don't need money.

I'm the same, except I will also sometimes spend the time going through the junk lists at the general traders for stuff that has components I use a lot. Depends on my mood, or if I'm in the middle of a build project.