Barrel choices are limited at this time, triggers dont have much of an effect but as far as upgrades for the .50 cal guns that are out, there doesn't seem to be any at this time.
You'll need to get a .50 cal loader, depending on how much you pay it may cost you more to get the equipment than what you'd end up saving so you might want to look into it a little bit before making the switch.
also realize that you may not be able to get the .50 cal paint at your local store with out special ordering it in advance.
It took me about 4 cases for the .50 cal to pay itself off for me, and then I sold the conversion kit & loader when I was done with it, so overall I actually saved a lot of money.
It'll be harder to resell a .50 cal spyder / entry level milsim then it would be a regular .68 at this time so I wouldn't count on being able to get any money back on the gun in the future if you decide you dont want it anymore