if you have the ability to buy the angel upgrades, then wait until you have to wait to get enough cash. spending on +50 newspapers at the start is worth a lot less than spending +50 newspapers when you are over 700 and trying to edge them up.
some suggestions : 1- if the purchase item is capped, then disable it rather than displaying the 'next' upgrade values that cannot be purchased. 2 - the 'level' quests, make these slightly quicker, as it is painful to have both the quests but need to wait for ages to get to the required level, and when this happens, people will just leave.
how to earn mega cash : in windows click on the rock, then press tab, this will scroll around the board. when it is on the rock press the space key and keep it down. it replicates a mouse click, but a LOT more per second. just keep this until you get bored :)
some improvements : Choose what the minions focus on, cash or bonus. Annoying having them pick up coins when you have levelled up and have £25k coins in the bank , but need bonus to get the score up.
Have some bonus' set to appear once. having the pierce bonus multiple times is no use (unless it only goes through once), and does the minion x2 double up if oyu have 2 of them?
More upgrades, as above the cash just piles up with no use after you have all levelled up.