Spent 280mil today, got 6 cards and a hand cramp. Something like the synergia is a brilliant idea. Fixing the loss of spirits for 3+ heroes, also a great idea. I won't comment on the dev (no need for plural). I'm sure once he gets back from his annual 6-month vacation and cures his arthritis, things will be running quite smoothly.

Edit: On average I get about 4-5k spirits per 100mil credits. The cards are pretty much moot.