Currently all mushrooms just give more points, but you could introduce mushrooms that spawn more rarely, but grant special power ups, like increased move speed, increased multiplier and so on. There could also be more interesting things like upgrades that make it so that occasional "bad" mushrooms spawn, but for buying said upgrade other spawn rates are multiplied (maybe in the vicinity of bad mushrooms).
In typical clicker fashion, you could also add helpers that occasionally collect some mushrooms (maybe those helpers could also have scenes with the character, for example as a reward for as certain upgrade level).