Although I use a light action, I am not sold on the idea that light springs allow you to play faster.

There is another school of thought that stiffer springs will allow the the "flappers" to return faster and that will allow you to play faster.

Frankly the two things that have made the most difference to me are
1) learning never to take your fingers off of the buttons. Many beginners take thier fingers off of the buttons and the hammer them down on the buttons. This slows playing quite a bit.

2) Checking your button height.
(How far do your buttons stick out of the fingerboard?) Having buttons too high will show you down. Having buttons too low will make your playing sound "mushy"

DP

DP has it right on explaining spring tension. Light action does not make for faster playing. The strength of your hands and fingers has to be considered. To that I would like to add that spring tension should be set when you pick your accordion up from its builder as was done on my Cajun accordion built by John Roger in 2005. The tension was set using weights. You can't get that with cookie cutter accordions.