Update: there is no more interesting stuff, as of level 165.
Viewing post in This Game is Addicting comments
Notes: Always pick [Gold Find] when it shows up. (Goldfind+ is better than even BetterUpgrade+++)
Always pick [Better Upgrades] if Gold Find doesn't show up.
After you hit like 30-40 levels in goldfind and better upgrades, you get a new upgrade basically every 4 clicks, your income literally outscales the speed the levelup slowdown is.
and if you avoid AOE upgrades (even one is bad tbh) and have ok-high [HP-regen] you just never die.