Eight Gates is well-known to be an extremely time-consuming power-up. One can sit and click for 3 hours and only get a handful of red stones. Perhaps that is part of the game design (a power-up that costs time more than coupons/ingots/activity). Provided that is not the case, I suggest the following.

Allow someone to let it run continuously until a stone of a certain color appears, e.g. stop on red, or stop on purple or higher. New stones would be collected into the highest stone automatically, stopping if that stone hits max level. Obviously it would also stop if you run out of coins.