Yes, you cum quicker when you haven't jacked off in a while, because your body hasn't experienced that stimuli as recently. And yes, your ejaculations are more forceful and plentiful too. This is because the fluids that make up semen (produced by the seminal vesicles, the prostate, and other assorted glands) aren't being diminished as often as they were before. It's like a garden hose. Stop water from exiting, and you'll have a bigger burst when you open it again.
And, like Silvertip said, your nuts do next-to-nothing when it comes to semen composition. Volume is mostly due to the seminal vesicles.