How much $$ spent becomes too much?
I lasted up until level 70 with 4 builders only spending 5$ for the 500 gem bundle. On a side note I find it a joke/scam they charge tax. You don't see prepaid game cards require you to pay tax..
Just recently got the 2500 gem bundle for my fifth builder. I deemed it was worth putting 20$ into this game after playing on and off since October 2012.
Time is also money; if I'm spending so much time on a game I'm already losing $$. So I don't believe in the "I'll play for 100+ hours but not spend $$" unless it doesn't effect game play. IE: LoL skins.