Welcome Prince Rupert,
So the Cav 32 is a mast head rig with a massive headsail and a small main. Your objective is to improve performance in the light?
From a financial point of view, I would think extending the boom (which effectively requires a new boom) and getting a new, bigger main - this is likely to cost easily twice as much as a new headsail. As IT says, mains are a substantially more complex sail than a headsail.
Not a lot of modern boats have the big headsails and small mains. We've got a Birdsall 37, and while the ratio's aren't as extreme as the Cav 32, she enjoys a big #1 and modest main. This type of boat are driven by the headsail. The main is more like a trim tab, it can be used to control the slot (between the sails) which dictates a lot of the performance, and the main can be used for adjusting balance and trim of the boat.
In short, if you want to improve performance, spend the money on a new headsail.
You've commented it doesn't have much life in it. Being new to the board I don't have a handle on how much experience you've got, but there is a massive difference between physical life and shape life. If it is a dacron sail, the physical life will be good, but the shape will be like trying to fly a sack of potatoes. The difference between an existing sail with poor shape and a new sail will be like night and day, you wont recognise the performance of your own boat. We did this on our boat a few season after buying it. The sails were old but "structurally fine". We had no power, but when the wind came up a little bit we would just heal over, so we'd reef, so we had less power, so we'd just get pissed off. We put on a new main, which, until you've felt the difference in performance looks like a cost you can't justify, but man, all of a sudden the boat would accelerate forward and not heal over. We could carry the full main 5 or 8 knots further up the wind range before reefing, the boat would be balanced, and much, much faster.
Also, Southernman's comment on getting some advice on rig tuning and sail performance. Correct rig set up will make a good difference to performance. But also understanding all the rig and trim settings for different wind conditions, windy with flat water, windy with lumpy water, light with flat water, light with lumpy water, they all reuire different sail shapes, and understanding and getting those right will make a massive difference to performance.
Oh, and putting on a longer boom may shift the balance of the boat and screw up the trim and balance. It is likely to shift the centre of effort back, which may lead to the boat trying to round up. I understand Cav 32's are renowned for their balance and light helm, wouldn't want to risk messing that up.
Black Panther who lurks around here used to do some sailing on a Cav 32, around the Pacific NW, or the world or something, I get mixed up. He may be along soon to comment. I think his Cav had the taller mast to keep it going in the light.