I don't find it's usually worth it to augment at all. The trade-offs you get for doing so almost exactly balance the return, so it's not generally helpful, in my opinion. There are some niche cases where you might want to do this: If you have a good enchantment on the weapon and want it to trigger more often, you might augment with speed; especially so if you have a +2-3 ring of accuracy. If it's a particularly quick weapon by default and has a lot of upgrades, it might start making sense to augment (though I haven't tested it, I doubt it). You might augment for damage if you're confident you can consistently perform one-hit kills and are not confident you can survive in a straight-up fight, but this sets you up for extremely messy failure if you do find yourself in such a fight.

As for whether to SOU, I'd take 2 more into it, then hit it with the upgraded Scroll of Remove Curse (whose name I forget) that you can get from the cauldron. When your item already has +6, those upgraded remove curse scrolls are more powerful than SOU, providing +2 levels per use. Make sure you save at least one remove curse scroll to get rid of the resultant curse on your item.

Before you do anything to that glaive, though, you need better armor. +1 chainmail may start to fall off soon.

Something that took me a while to figure out: If you find a shrine of healing, it will remove the curses from all of your equipped items as well as fully heal you. You can use this to your advantage by just equipping all of your unidentified items next to those shrines. If it gets cursed to you, no worries, just step in the shrine. If not, your item sells for a bit more now. Be advised, equipping takes a several turns, so if you're low on hunger just skip it or check the most important items.

Small nitpick: It's Aug Ment, not Ar Gu Ment.