Sir Masters got me thinking, and he's very right. However limiting the availability of high end items on respawn would just serve to make for boring low threat enemies.
To go along with my previous post, a nice wrinkle might be a supply and demand system to traders. After you sell the gun runners 10 Lasrer RCWs the price they offer would be cut substantially, as they would get overstocked. Set a rate at which they might sell certain items so the price slowly rises again. I'm sure they would sell more hunting rifles than AMRs so you could sell more low tier items before the price degrades, but high end prices would degrade quicker due to slower sales.
This allows the barter skill to keep your selling prices higher and offset the degradation without the need to strip the high end items from enemies.
Though programming all that would probably be a pain in the ass, Then again it worked in M.U.L.E. and that was a Commodore 64 game.
The way things are set up, the only way to 'shut off the tap', so to speak, is to not have respawns in the first place, which would have the side benefit of making any area you pacified stay that way.
The main problem with a supply-and-demand model is that the player is the only one 'demanding' anything. As such it would be incredibly easy to abuse, since you could get the price benefit of 100 Barter by repeated use of the 'wait' function to sink prices through lack of sales. You would need to implement a hidden mechanic that kept a tally of 'virtual sales' and used it to adjust the available items daily to reflect 'normal' business.
One way to put a brake on price alteration tricks would be to have the above mechanic not only adjust the prices but whether or not the item is even available. This is already done to some extent by the restock mechanic, which rolls against a chart to see which of the better items actually shows up for sale from their leveled lists, however that doesn't take anything other than that roll into account and is readily manipulated to get the stuff you want. Tying the restock into the 'virtual sales' tabulation would further adjust what's available and for how much.
Since there is only ever one copy of any given T5 or T6 item for sale at a given vendor during any one selling period (i.e. time between restocks) unless their lists are weighted, these items would be more likely to either get insanely expensive or not even be there. The problem here is that you risk developing a case of Elder Scrolls Pricing Syndrome?, wherein you have to sell everything you own for a single item from the next tier up due to how loot availability works, so there would need to be an upper bound on how high the price of the really rare stuff could get.
If the 'no respawns' method is used, then the prices on the best stuff do not necessarily need to be really high since you won't be able to just grab 3 Plasma Rifles out of your stash of 47 and go shopping. Rather, those 3 Plasma Rifles would be incredibly valuable since the odds of getting 3 more in full condition would be really low unless you're abusing the Vending Machine for Weapon Repair Kits. This would apply even more for higher-end armors, since you wouldn't be able to farm, say, NCR for various 6K-cap Combat Armors as the supply would be strictly limited. Sure, there would be the 'golden age' where there was a massive inflow of really valuable stuff, but once that ended you'd be rather hard-pressed to afford more of the high(er)-end stuff for repairs due to running out of items to trade for it.
A smart user of Jury Rigging could still turn a decent profit by buying up the damaged armors, patching them up, and selling them off, but he/she would be using up resources that are, themselves, finite in the process, so that would only go so far.