New Reno Arms is a buggy place in general. If you unlock the back door, the NPCs do go through the fence. As mentioned, asking Eldrige to upgrade after finishing the game will make him wig out on you. I _Think_ that if you have a particularly high barter skill, he will do upgrades for free... I know that some poele do, though. why is this useful, if Algernon does them for free, also? Because you can barter with ihm and use the "Barter Trick" to get infinite upgraded weapons and thereby arm your party with a lot of good weapons if you care to.
I'll explain. Superior forms of weapons are totally new items. The old one are not upgraded, but rather *replaced*. If you ask for an upgrade, then one text level before actually paying, enter barter, and drop it, then leave barter and agree, the game will give you a new weapon full of ammunition. The old one will still be on the floor. Pick it up and repeat until you've got as many of the weapon as you please. This trick has far-reaching implications wherever you pay for something in dialogue from someone with whom you can barter.
Furthermore, there are some notable items to be found laying around the place... upstairs there's a 9mm Mauser pistol (Better than a 10mm but when you get it it's largely useless), and an NCR Holotape that you cannot actually use. A dog blocks access to a container which I think has some items, but they're not worth the super-stimpacks it'd take to wipe out the dog. Downstairs there's all sorts of neat stuff, but the only one of note here is the Easter Egg, an item that was supposed to have far-reaching uses but now does... nothing! But it's funny.