pulsetalent the big thing in my opinion would be tempo change ST3 can nicely speed up or slow down your performance to find that perfect sweet spot that suits that moment in time, but if you are happy with how you are running there isn’t much to gain except the backup feature and the fact all your files are neatly placed in the ST3 folder where you have nothing to do with iTunes or Music which is a blessing, I would get ST3 and try it on the side and see how it works for you as it is a lot more complicated and and loaded with features, but you can ignore them and run simply if you want.
Good luck!