I think I found a glitch: you can't buy upgrades when adventurers are on quests, but you can buy them with the 'buy all upgrades' button! It's small, but it's something.
Could you maybe change the colour of the Upgrades Available icon depending upon if its an Angel or a Cash Upgrade? Also, please move the Achievements Icon to somewhere else, it currently blocks the Donut Shop icon.
I understand it'd be hard to do, but I would really like a way of buying a set amount instead of having to click so many times. Maybe make a buy times x button?
Thanks for the report. :)