Currently, the Trader offers a few items of note:

1. Megingjord - belt which offers 150 carry weight. Pretty much mandatory if you aren't a fan of the Cart.

2. Ymir's Flesh - used for endgame crafting.. and you will need more than one of them.

If you don't care much about that carry weight, or the weapons crafted using Ymir's Flesh, then you can by all means skip out on the Trader.. although I do believe an update for him is planned at some point. As to what that update entails, I have no idea, but I assume he will get more endgame-related items, once the endgame shifts beyond the Plains.

The other stuff the trader offers is mostly cosmetic, but there's also a head lamp item if you do anything at night that requires light. I typically don't, nor do I have trouble seeing in Burial Chambers/Crypts, so I never felt the need for that item.

It is kinda neat, though, and if we had a proper Cave/Inner-earth-type biome, I would probably recommend it.

Edit: oh, also, he offers a fishing pole and bait. Sadly, it currently isn't the greatest/best way to obtain food, and by the time you can just casually visit the trader anything fish-related is out-paced by the current biome's food.