The percentage sets are the worst. Upgrading them to gold won’t make the percentage go up any. Weapons...even in bad trait are first priority. Even better now with transmute

You generally (with a few exceptions) want to have gold gear in end game content ... to be the best for yourself or your team:

Vet Trials
End Game PvP
vMA
vDSA

Upgradiygear to gold is min/maxing. Unless that's your goal there is little need. Mostly ic your trying to push yourself to be all you can be in PvP or PvE.

If it helps, here’s the very rough numbers on what upgrading from purple to gold gets you.

Weapons: this upgrade is quite significant and you should expect to get a lot of power out of it. The boost to the weapon’s damage rating is about 20%...which is a lot. You can quasi-test the benefit to your character before upgrading. Equip the purple weapon then go hit something large with and without major brutality (if stam) or major sorcery (if magic). Take note of the non-critical base damage values for either. If, for example, an ability hits for 7500 and 9000, the 20% boost to damage is giving you about 1500 more per hit. Making that weapon gold would add at least that much on top of those values.

(Or ignore the math and just trust us that gold weapons are worth it. Not everyone has to be a math nerd out smacking mammoths on the butt to record damage values.)

Armor: each piece upgraded to gold gets a 3.5% boost to the armor rating. This is a marginal boost, but when all 7 items are gold it’s about a 25% increase. For the most part, I always recommend waiting until you’re c160 and have sets you love and know you’ll use, then upgrade one piece at a time as you can.

Other buffs from upgrading to gold:

Enchantment: upgrading doesn’t affect the max enchantment you can put on gear - a c160 piece has the same max whether it’s purple or gold. However, upgrading a drop set with its original enchant automatically increases the enchantment value...in effect saving you from using a kuta to make a new enchant. Crafted pieces won’t change their enchant value as you upgrade the gear.

Trait: the trait value will increase. This is pretty significant...as an example, a piece with divines goes from 6.5% boost to 7.5%. So a full set of gold gear in all divines would offer a 7% add’l boost to whatever mundus you run.

Set bonuses: these also go up, but the boost is pretty minor. And remember, the values listed are spread across the pieces of that set you’re wearing. For example, a set of purple set gear with a weapon crit buff offers +804. A gold set offers +833. Upgrading each piece will add about 6 to that crit buff...you don’t get +30 for each piece.

5th trait bonus: as other have said, sometimes gold increases the buff from these bonuses and sometimes it does not. Look at the tool tip in the upgrade menu to see how your sets are affected. Generally, buffs that offer a numeric value do get a boost, while percent values do not. For example, Hundings Rage offers +300 weapon damage. That’s a numeric value, and moving to higher quaLity does increase the value. Marksman offers a -5% cost and +8% damage buff. Those are percents, and a white piece will offer the same buff as a gold.

So:

1. Make sure you’re c160+ and wearing c160 gear.
2. Test it and find the sets you like the most.
3. Upgrade the weapons first, test some more.
4. Upgrade each piece as you find you need to be stronger.