I think it is people are more used to having a gun to carry in SA with a manual safety..so the DA/SA version fits that better..
also have heard the DA/SA version is easier to work with and tear apart..because the decocker has a few more springs, etc..
but have heard both Angus and Matt will do action jobs on decockers now..
so as far as upgrades...
new sights, competition hammer, nice grips, more mags, new springs. lots of options...
enjoy your new gun..