First, sails make a huge, and I stress HUGE, difference in pointing ability. If your sails are old, no matter how they may look, they aren't performing that well. You will be amazed at the difference new set of sails will make.
As for the rigging, buy a Loos gauge, from WM or anywhere else, it's worth the investment. They come with a chart with a recommended range for a given shroud size. Follow the directions and make small changes from side to side until everything is where you want it, and this will cure a lot of the unequal port vs. starboard performance. Many boats sail slightly better on one tack than the other, however. There are just a lot of variables involved, and I wouldn't worry about minor differences.