I have two SIG P320s, a full-size in .45 ACP and a compact in 9 mm Luger. Both went in for the "voluntary upgrade" but not at the same time. I sent to .45 in first and compared it closely to the unmodified compact after it returned.
Before the upgrade there was no appreciable difference between the two triggers. After the upgrade I compared the two pistols in dry fire many times. There was no doubt that the pull weight for the modified trigger was a little bit lighter, although the difference was not dramatic.
I then sent the 9 mm in and when it came back compared the two side by side again. Now there was no appreciable difference in the pull weight of the modified triggers. So both were a bit lighter than originally.
I too would have preferred the pull weight of the original trigger. But in retrospect, the change was not great enough that it would dissuade me from going ahead with the upgrade.
The modification also includes the addition of a disconnector. I have seen some posts from extremely knowledgeable shooters who claim that they have seen definite incidents of the original P320 firing out of battery. SIG claims this was impossible with the original pistol but I have my doubts regarding their credibility. I have not seen any credible accounts of the modified pistol with the disconnector firing out of battery.