If you earn 3000+ euro or $ , spending ~300 per month isn't a big deal, especially if you don't have to pay any debts, etc. The deals are sometimes pretty bad, but there are ppl who could buy even whole game if the wanted to. Besides I think some of the devs are playing this game too with lots of free stuff, just so they can create the "chase the bunny" effect, where players need to keep spending to have a chance against the fully stacked devs lineups.
BTW the raid all button which consume all ur stamina seems to give less rewards than if you raid it 1 by 1. I suspect there could be some internal CD which doesn't allow specific items to drop more than every X sec or min. This can be easly tested in elite campaign where default tries is 3. If you do all 3 in short time for 100 different towers you will get max 2 soul stones drop every ~30 towers if you are very lucky. Now if you raid it 1 by 1 and stop for several mins every time you get soul stone drop , ur overall amuont of soul stones received from the same amount of stamina will often be ~20 - 40% higher. At least this is what I got from my experiments.