Re: new 120% genoa
It really depends on what your priorities are. Are you going to campaign your boat seriously? Are you and your crew at an elite level where the incremental improvement that you get from the hottest racing sails is going to be noticeable? Or are you just looking to go out and hone your skills with beercan racing?
What a lot of casual racers do is buy a good, durable dacron mainsail, and then go with a good laminate headsail for racing only, and use their old sails for cruising and daysailing. Sure it doesn't have the cool factor of having a matching suit of high tech sails, but it is a more practical solution if you are on a budget. Remember, modern dacrons are very high quality and will last for many years. They will not be "bagged out" after a couple of years! They are very low stretch materials too. Mainsails do not get nearly as much punishment as a headsail does, and they tend to be built out of heavier cloth.
When it comes to racing laminates the goal is the lightest possible sail for a given strength, and they do sacrifice durability. A more expensive sail does not necessarily mean more durable or longer lasting; often the opposite is true! The most expensive racing headsail you can get will be ruined very quickly just by using it in higher than designed wind speeds!
With regards to what size genoa you should get, it really depends on what the prevailing conditions you sail in are. Your handicap will be adjusted based on your sail area, so you will rate slower with a smaller sail. In some cases it may even move you into a different division, so you should run the numbers by your handicapper and see what it does for your rating. I couldn't speak to what the optimum sail area for your particular boat is, but typically racers go for the maximum sail area they can carry. A larger sail will not give you balance problems such as lee helm as some have stated. Such problems are a factor of rig tuning more than headsail size.
1979 Santana 30 Tall Rig