George, that's not such a simple question. Let me illustrate. Let's suppose you've aready got sufficient return air to have a -.02 RA static. But the air filter is plugged solid so the RA statis is now -.08. Adding another return won't change that reading at all because the problem isn't lack of RA outlest, it's another problem in the system. Adding another return to an undersized duct for example, won't change the static. Adding 10 more returns with huge ducts won't change the total static if the supply side is undersized and/or restricted. So you see, it's not just a "yes" or "no" answer. Static is really the 'bood pressure' of the system and just like in the body, the entire distribution system is part of the problem and all of the solution.
If YOU want change, YOU have to first change.
If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!