With the current upgrading system, which makes it close to impossible to fully upgrade an item to it's maximum potential, hence making it feel like never really reaching the end goal, and the high prices of stones proofing the abundance and rarity of the stones, I feel like it makes this game's end-game suffer. Like in most MMO's, once you hit the level cap, all you can do is focus on your gear and get better at PvP technique-wise, right?
If either upgrading were made easier or the stone drops would greatly be increased, more people would be able to have some sense of progression in the end-game. As I see it now, getting +15 is impossible for too many people, drop rates of stones are low, and the lack of progression in the end-game towards reaching the very end-goal, which is getting fully upgraded gear to perfect your character, seems so unlikely that the game itself would eventually suffer from it, because it would get plane boring and pointless quite quickly when you hit cap level.
I've little experience tho, so maybe my opinion is flawed, but still. I think most would agree that upgrading gear and making your character stronger even after hitting the level cap is something, if not the only thing, that's 'fun' to do in the end-game(like in most MMO's) and would keep them playing, if it were made a bit easier than it currently is.
Additionally, I'd rather have an increase in stone drops than a change in the upgrading system. Using stones, upgrading gear is somewhat exciting/fun, cause of the low chance of success and gives players a sense of accomplishment when they succeed. To be able to do that gamble(upgrading gear) more often would make the game more fun to play. A great increase in stone drops won't kill the game, since getting stones isn't even half the job. There's still getting the gear with the right stats and the upgrading itself.