Most racing of Widgeons is done as "One-Design", that is all boats in the race are Widgeons. They are still a very popular boat for Junior Racing in Yacht Club and sailing school programs.
As far as rigging tension, she is a 12' small boat, "tuning" the rig will basically just mean taking the slack out of the wire. You don't want to overtighten, just "hand-tight" according to the manual.
The info that I have indicates a Portsmouth Number of 121.6
I wouldn't go overboard with racing upgrades, besides keeping the hull bottom smooth. Any gains due to extensive race improvements will still result in at best, minor speed gains.
Maybe new sails, but again....... the Widgeon isn't exactly a "HOT" racing class. Most Widgeon racing is in the Junior Programs at Yacht Clubs.
I think that best advice if you want to race (assuming you found a group to race with/against) is the old; PRACTICE, PRACTICE, PRACTICE!