I never enhanced anything past +4 until lvl cap, haven't had an issue leveling
But like do you really need beyond +7 to clear content? Or it just makes it easier?
I couldn't solo maniac until I had at minimum a +4 weapon. Getting higher makes it exponentially easier. I started to struggle with my +5 21 wep around Wolf Cry, which is when I upgraded to a +6 32 and breezed through again. Pre-bought the 40 stuff because these sets (16, 26, 40) are all very powerful in comparison to other gear and I had skipped the last 2 (sans armor) out of lack of funds. Only need armor to +4 for bonus, if even enhanced at all.. but I like having a safety net due to poor netcode/laggy servers/clustertruck of enemies/steel graves. Expected this to carry me to 55, which is why I invested so much into it.
I tested out enhancing lower level weapons (pre-10) after posting. Gotten to +7 numerous times before breaking, even 1-6 100% multiple times over. Either I had atrocious luck on my 40 gear, or the difficulty to enhance higher level/rarity stuff goes up a lot.. probably both. All but 2 of my ~15 protected enhancements so far would've been destroyed by comparison.
Regardless, it's still an awful experience, and now I have to grind and bust my ass to get back everything I've lost from this. Sure hope the rate of acquisition increases dramatically as I level up more.. can barely sell anything on the market, and if you do it's pennies unless rolled well.