If I have 30 people dividing it into two teams of 15 won't change how much resources I have
Who said anything about dividing your total resources in half? How does the ACTUAL size of each project come into play? If one or two community members without the source code can come up with sizable, functional patches, then why couldn't say 5-6 WITH the source code, and considerable development experience. One guy added mouselook and resolutions higher than 640x400 to the original System Shock with no source code. There are so many variables here (aside from just the numbers you chose.)
***I did catch the but I thought I'd give a few reasons why I don't think it's at all unreasonable.