unused Weapon & Armour slots
Unless the item in question is one that you’re going to replace very soon, I’d always insert upgrades into your gear if available. The bonuses from Runes/Sigils etc. can make a LOT of difference to your gameplay.
If money is tight, you can get by on Major runes/sigils or Crests until you’re ready to do a final gear upgrade.
There are some incredibly cheap runes/gems/crests around on the trading post (cheap because they aren’t great) but can be fun to use while levelling, and they’re going to better than nothing.
I tend to just keep upgrades from salvaging greens/rares..
If you’re wearing blues or whites, don’t stick anything into the upgrade slot. Upgrading them means you can’t sell them when you are done with them.
Unless the item in question is one that you’re going to replace very soon,
For me, I upgrade my characters gear every 5 levels. So, until I get to 80 and buy exotics, all the gear will be replaced soon.
Though I have found one oddity on the TP. At the levels where I buy greens, I often find that a green with an upgrade is cheaper than one of the same stats without the upgrade. So I usually buy those with the upgrades inserted.
I thought it was kind of a given that when you’re upgrading gear, you should always go for Masterwork quality as a minimum (good benefit/price point if you’re being frugal), but yeah, good point about the Blue/White gear.
The sigils/runes will prove to be far more of a ‘game changer’ in WvW than PvE.
Minor/Major for PvE is fine, definitely want Superior for WvW.