Stepper,
Two thoughts.
First of all, if the Rebel Baler you are looking at is a model 5400, Vermeer recommends only a minimum 40 HP tractor. So, you may very well be fine with your current tractor. If you are looking at the 5500 Rebel, that takes a 55HP tractor which means you may need to trade up.
Second, if you check the info on your New Holland 3930, I think you'll find it was probably manufactured by a company called Escort in India.
Escort now markets that virtually identical formerly New Holland 3930 in the US as a Farmtrac model 555. If you have been satisfied with your present tractor then you might check out the next size up from Farmtrac, the 52 PTO HP model 665. You'll find it quite similar to your current tractor (although the Farmtrac model is a platform tractor).
I've got the 65 PTO HP Farmtrac model 675 and have been quite satisfied. I find the Farmtrac line to be a good high quality tractor at an affordable price.