I'm at level 7 and item durability is getting really annoying. It cost like half my gold last time I had to repair my sword, but I did it anyway. I was back to full or whatever high percentage they repair it to. Then I did a night-wraith contract... and I'm back under 50% and in need of repairs. ONE FIGHT. The buggers regenerate and its really hard to seal the deal quickly. Really fucking angry right now. It feels like I have almost no money constantly yet I buy almost nothing but occasional alchemical supplies. Maybe I'll eventually be able to cash in these foreign coins at the bank or w/e but currently this is "financial stress and irritating group combat simulator 2015".
Did you fight the wraith(s) in a Yrden field? The first one I fought I chipped down without Yrden and it does a real number on sword durability to be sure, but then I read their bestiary entry and saw that they were weak to Yrden. From then on my strategy with wraiths has been to drop a Yrden between myself and them, keep on the opposite outer edge (rolling or dodging as needed) and when they enter go for a strong attach followed by two weak attacks. That first strong attach on a wraith inside a Yrden can take half or more of their health away.
Also, if it is a noonwraith or nightwraith capable of summoning three wraiths you need to go all quick attack (or crossbow if you have it) at them asap because they'll start trying to drain your life to regen the noon/nightwraith. I believe the black blood potion would solve this as well, not 100% on that though.
Other than that, if you go for a quest a good bit above your level what you're really looking for there is the payoff between damage to your gear and the quality of the reward. Three levels higher shouldn't be a big issue though. When first arriving in Velen I basically wiped out my silver sword on a level 14 forktail (type of draconid) when I was level 6 at a random "hidden treasure" and it cost me a good chunk of my money to get it fixed. Entirely worth it however as I got a pair of Assassin's Boots with two slots that I used for about 10 levels.
As the game progresses you'll find ample repair kits of all ranges from Amateur (15%) to Master (90%). I ended up just selling 25 master armor repair kits simply because I didn't want the weight.
An additional strategy for early game play with weapons, as silver swords are harder to find, is to keep all silvers you come across and basically use the weakest one you think can get you through a fight, then as they wear down below 50% sell them for a nice stack of gold or dismantle to build the next in line.