I just realized something...
Once you collect all of the daily mission characters you cannot collect any more stamps. You need to collect stamps to "unlock" the two other missions where your prize may be coins, pixels, or tickets.
You can use tickets to obtain characters that you would normally need to buy.
Once you collect all of the daily mission characters the "missions" button disappears. This means you no longer have the opportunity to collect coins, pixels, or tickets.
So you're basically stuck, unable to potentially obtain characters from the ticket machine, until the game updates and more daily characters are made available.
That's pretty crummy.