If your mainspring strut is rough, you will still have a gritty trigger pull. Ditto for the surfaces on the hammer and trigger that move against each other. My only SP101s with lighter springs are the ones worked over by Jack Weigand when he was still doing custom work. The rest of my SP101s were cherry-picked, with patience, at dealers, and I probably wouldn't install lighter springs in them if someone gave me the springs as gifts. I have handled revolvers with such light springs inside them that the trigger return was notably sluggish.
In my hands, with the high grip I use, I have so much mechanical advantage to work the trigger, I just don't need light springs, thus far, even with some amount of weakness caused by nerve impingement. I find the smartly-fast trigger return to be comforting when shooting fast.
Do be SURE to test-fire with your carry loads to make sure the primers will go off EVERY time. I did install lighter springs in my first GP100, an early 1990's gun, and had some failures to ignite magnum primers. I re-installed the factory mainspring, pronto, and reliability returned. This is my only workin' Ruger revolver thus far I have felt needed smoothing of the internal parts, beyond a bit of dry-firing, and I performed the task myself. (I have another GP100, a limited-run 5" gun, that I purchased without cherry-picking, as it was the only one I could find of that edition; I think it may need some attention to its internal parts, if/when it becomes a workin' gun.)