Since you use two springs only , I guess you use .008s gauge ... So putting more springs on the same gauge will make you shorten the springs' length by unscrewing them ... This can put them under no tension in case you raise the pitch too much with the trem bar, and springs may drop a little from their sockets , and they might not return to the original position , making you go out of tune.
I think you should give the "hipshot trem setters" a shot , even though they seem way overprized ... Hipshot spring $37.15 , Regular Spring $1.5 !!!!!