The lack of good faction neutral armor's is something that should be addressed in some future DLC. The best method I can think of is a workbench method to remove the faction identification from any armor (perhapse at the cost of a few DT or some other minor penalty). If you could then add/remove the faction symbols, then you could truely use the disguise system to your full advantage without forcing anyone to miss out on decent equipment because of the "shoot on sight" factions in the game (something I both love and hate at the same time).

I can understand the whole role playing thing but if you really want the armor drop the difficulty level and just kill a guy, loot and run away. You shouldn't be hated for just one death so as long as you can run away and quick travel all is well.

There's at least two mods available in the new vegas nexus that give you access to NCR faction armor without the faction tag, meaning you can use them and still use your normal fame values for interactions. There's also one for Legion armor (which, frankly, is a lot cooler, especially the praetorian one).