hey, nice to hear your working on the upgrade system.
the good thing on the actual system is that its really hard to make your stuff +15, on the other side the fail rate is frustrating and its too much based on luck playing much should be more rewarded.
i think +15 is not a good number for the highest upgrade
the problem is if you increase the succes rate its gonna be to easy and everybody get +15 in short time,
if you dont increase it its pur luck and people may fail 100 times in a row thats bad too.
i hope you like my idea.
increase the max upgrade from 15 to 75
decrease the upgrade effect to 20% of the actual amount
rate 1-15=100% 16-50 = 50% 51-75= 33,33%
Break:No Fail=still -1/white stone protect the downgrade.
there could also be a middle way like 30-40 max upgrades with adjusted upgrade effect
with that changes its still a big challenge to get your upgrades but less frustrating succes rate farming days/weeks without any progress feels bad, that way we can have a little progress every day playing.
i would also disable blackstone drops and make them available on a vendor/ purple/green stones give + 2-3 on succes
in that case stone droprate should get a little buff too but not much.
edit*
didnt notice this thread is from 2015 if you still care to change it i would like to hear how you think about that idea.