sadly plussing to +3 is like 90% chances, then to +4 seems to drop to 40% and as for +5 you seem to get a 10% chance, don't even think about +6 lol. Sadly if you spent 2000 diamonds to plus wings, that is a pretty sad story. I have been using the wings for 5 years, once in a while, clean off the stats and put new stats on, 99 diamonds for an attribute purifying stone and done.
If you expect to get new gear and wings every new level cap, you are the only person to blame for making poor choices. People don't buy diamonds ONLY for plussing gems but then again what do i know, i am a smart noob.
Sadly unlike Frogster, Gameforge runs it more like a business then a game, profit margin is all that counts. They have FREE GM's, that get no salary etc, they deal with all the crap we dish out on the forums and QQ's. Stop expecting changes, it will not come.