The comments (I won't say any specific names...) about an upgrade dealer "ruining the game"(!!!) and making it so that "none of [us] have to actually play the game to get what [we] want....
[we] can just go buy it" (lord forbid!) really make me laugh. We'll never have to leave town again, traders will give us upgrades for free!!
But anyways, yeah, /sign to the upgrade trader. The best part would be that, like with the rune trader, I wouldn't have to farm/spam WTB ads
forever for upgrades that aren't very popular, and thus are seldom available. Players could also use the trader as a reference for sales prices.
As for the weapon trader, exactly what are we talking here? A trader who simply vends every weapon type in the game, allowing gamers to buy whatever design of weapon they want, would be horrendous. That'd be like having universal armor craftsmen who allow you to buy whatever armor you want where ever you are, atleast in my mind. Part of the fun of getting a weapon is having to defeat the enemies that wield that wield that type of weapon, I think.
um...and, if you didn't know, we have weaponsmiths (or collectors, alternately) already. Upgradable/inscribable maxed out weapons of most varieties can be obtained from these already extant NPC's.
However, upgrading weaponsmiths so that they can craft differing styles of weapons sounds like a workable idea to me. This would perhaps even add a more natural feel to the weaponsmiths: to obtain a particular style of weapon, say a sickle, one would go to a Krytan weaponsmith, similar to going to Droknar's forge to obtain the armor design of the armorsmiths there. More common designs could be available at all weaponsmiths, like butterfly swords or long swords, and, of course, unique or very rare designs (like mursaat hammers or Victo's weapons' skins) would remain unavailable at craftsmen, or available at extremely high prices. I can't imagine this being too difficult to implement, either, as armorsmiths are already available. They wouldn't be adding any new features, they'd just be adding the additional weapon/shield designs, as well as perhaps a few more NPC's. Although my description is quite rough, I believe the idea is clear enough.
Also, see
Making Weaponsmiths Useful. Although this suggestion is more geared towards making rare skins more easily available, it is rather close to the idea suggested above.