Getting the "you don't have an old model vaquero, you have an old style, large frame vaquero" out of the way....
This is a tough one to answer without sounding like a snarky jerk. (I know, too late) They're real easy to do action work on, but if you had the ability you probably wouldn't be asking right?
I've tried a few reduced power main springs and trigger return springs over the years and ended up removing all of them and throwing them away. I did not care for the slower lock time/hammer fall. You will see some people laugh at that, say that they use them and don't notice any difference. I have no doubt that that is true, for them. But that says more about them and their shooting than the guns/springs.
One FREE thing you can do is tune your trigger return spring. It costs nothing and will do a better job than a reduced power one, which can feel mushy or hang up resetting.
http://www.cylindersmith.com/triggerspring.html