If I had a vote, I would cast it in favor of keeping the Sigma stock and shooting lots of rounds through her. Liability and RE-liabililty issues are primary reasons. Plus, time heals most issues with the Sigma, or at least that's what happened with mine.
After six years of use, I have an honest 4,000 rounds through my Sigma 9VE. I have to admit when it was brand new (and so was I), I put more lead into the ground in front of the target than I did into the target, due to a stiff trigger. But now it's like falling off a log--good defense groups with any kind of ammo--never a hick-up. Plus, I have experienced at least three side benefits to taking time to learn my Sigma:
1. I can shoot a snub-nosed .38 or .357 Mag. with ease now, because the Sigma trigger pull is very similar to a double-action revolver feel.
2. I feel very confident in carrying my Sigma with a round in the chamber, because I know that long trigger pull and the automatic trigger safety (along with safe handling practices) will prevent an unintentional firing accident.
3. Firing several thousand rounds has smoothed the trigger action on my Sigma. After the first 800 rounds or so I could feel a slight difference in the trigger, but the real benefits didn't break in until after a couple of thousand rounds.
I've tried a few things to improve my Sigma. For a while I used a stiffer recoil spring for +P ammo, but I found it unnecessary, and I've considered the "trigger fix," but I really like my trigger now. At this stage of the game I can honestly say I love my Sigma as she sits--naked, with no modifications. I take her with me for every day carry most of the time, for bowling pins, and for plinking and hiking as well. In the interest of full disclosure, I do use a home-made rubber grip (made from a bicycle inner tube) for extended sessions. I also carry two of the "Military and Police Only" 17-round magazines. Other than that, all I can say is, "Wow!" What a difference time and practice made!
Whatever you decide, good luck.