I don't know about limit for quality, but I believe there is like a limit for money(2.15B)
Yes thats true, someone made a post on the forum about this about the beginning of the season, 2.15B or 2,147,483,647 is the max because any higher is signed 32 bit overflow and the number would go into minus.
03-07-2013
Shadow
I wrote to support they told me that they are working to extend this ammount cause I 4 seasons in a row reach max 2.15B.