Lots of people have converted to other braking systems. You don't have to spend a lot of money to improve it.
Vacuum is cheapest and is probably the easiest one to to. You do need a brake pedal from a vacuum brake equipped g-body, though. There are great kits from vendors like
G-Body. Everything you need is in the box and they work great if you like vacuum brakes. Basically, you are buying a booster, master cylinder, pedal, hose and a new billet vacuum block with an extra port to supply the booster.
Pros: easy to install and parts are everywhere
Cons: some people have trouble holding boost at the line, but a healthy braking system with minor upgrades work for most
Hydroboost can be done for under $300 and it retains the factory powermaster pedal. There are
complete kits available from places like Powerbrake-drivetrain.com but they do seem a bit pricey. The install isn't too bad but it is more difficult than vacuum since you have to remove the alternator and a few other things to get clearance to run pressure hoses for the hydroboost. The upside is GREAT pedal feel and increased line pressure for great clamping force with an otherwise stock braking system. Having driven both vacuum and hydro equipped G-body cars, I prefer hydro because of the performance, feel and response of the pedal.
Pros: superior line pressure and great pedal feel. Racers can hold lots of boost at the line since no vacuum is required for the assist
Cons: a fairly challenging install ; requires a healthy power steering pump and clean system
Powermaster systems can be replaced with a rebuilt unit too. They are expensive at $500-$650 or so, but if you take care of them they will take care of you.
Pros: Originality ; ok, can't think of any others.
Cons: Basically anything that breaks is expensive! Frequent care can keep 'em alive, though.
It all comes down to what your goals are and how comfortable you are with making changes to your brake system. All systems work well and have their pros and cons. Whatever you do, be aware that you can always go back to Powermaster if you ever want to since none of these are irreversible. Just realize that if you convert and then go back to Powermaster for originality, you will be replacing the accumulator ball to the tune of $180 because they do not like to sit around.
I have a complete writeup on a hydroboost install in my sig if you are interested.
