I can agree with Steven Miller and most other people saying that adding some mass will be beneficial to jumping, but what I failed to mention was, what about for a single leg jumper?  
Idk, I've always read that, single leg jumping has a lot more to do with leverage, lower body weight, etc... While double leg jumping has a lot more to do with strength meaning added muscle mass (+strength) can only help.
I mean besides Lebron James, cause he's a freak of nature, most great single leg jumpers I've seen were very light/lean/skinny.  My friend on my intramural bball team who dunks on opponents on the regular is 6'0" 159lbs, and he has a 42"+ vertical.  Kadour Ziani, prolly the best single leg dunker ever, is very skinny.  
ALSO, are you guys saying that carrying excess body fat (10%+) has a structural disadvantage as well?  Like the fat effects your movement efficiency, COM, leverage and such?