if you go for event girls and fight darklord it pretty much is like 85-90% income loss (from boss battles only obviously), for edwarda it is like -60%, which is actually massive (with your calculations that would be ~150k - 750k instead of your 1.2mil)
its pretty stupid to think about, but trying for an event girl basically costs you 13-18k
I'd like to hear what your take on tower of fame vs troll fights (outside of events obviously) is? as one grants XP which does not have an immediate impact and one 'only' gives money