Financially, the T20 format may be important for the cricketers. But if they are more concerned about the fame, then they should not overlook the longer format. When someone talks about the stats (highest number of runs, top wicket takers), they always mention about these stats from the test cricket. I have almost never heard about anyone talking about the T20I stats.
I think all three formats of the cricket are important and therefore we see all the series consists of T20, One day and test matches. Each game has its own importance and give you entertainment. You will never feel bored if you are seeing a test match between nations like India and Australia.