I can't answer all of the questions, but I can hit a few.
Mast: Give me a call, I have a spare (straight!) comptip mast.
Rivets: Use a cold chisel to knock off the tops, then knock the rivets into the beams with a phillips head screwdriver. You can drill them out with a 3/16 bit, but you stand the chance of reaming the hole. I do a lot of drilling and haven't had a problem with enlarging the hole, but the best way is with the chisel. I use all 3/16" stainless pop rivets that you can buy at any hardware store.
Upwind sailing: The 14 is sailed best with a lot of mast rake. That and a new sail will make a big difference. If your sail is old and blown out, you will have a tough time going upwind.
Dolphin striker: Yes, install it! The Murray's one is what I installed on all my 14s--they are easy and they really make a difference!!
Jib: It makes it easier to tack and I find that downwind performace is greatly improved. Most 14 uni sailors sail dead down wind, but the jib lets you jibe like the 16s. I also found that you can't sail as close upwind with the jib, too. Since it was really an afterthought, there doesn't seem to be a lot of design to it, but I think it is a good system I'm converting all my 14s to Turbos.
I'm ordering a bunch of jibs at a discount, so if you want in, let me know.
Age of boat: One more thing, if they boat really is a 70's boat, it may not have the VIN etched on the stern. I have found that they stamped the production (sail number) on one of the pylons. If you see a number stamped somewhere, You can guarantee is is one of the earlier boats.
Racing: Check in to the Hobie fleet in Va Beach. We sponsor several races and had a good 14 turn out last year for our championships. Granted, I made my friends sail the 14s, but we had a class!
Hope this helps.