Would kind of speed increase , if any, could be expected by adding nosecones to a 32 Fever that runs 82 mph now.

At 82 mph doubt you would see any increase. There is a chance depending on who's nosecone you use, that you will effect the handling of the boat with a longer aspect ratio, and add more stern lift. Their is more to be gained working with Throttle up or BBlades and getting your props tuned to your exact application. It may take a couple of tries to get them where you want them, but in the long run you will be happier I think.

I'm content with the speed now, yet I keep seeing claims of 3-5 mph with cones. Looks like an easy project.

The only way you would gain speed is if you are experiencing prop slip due to blow out. You would have to push the Bravo gear case fast enough that the water starts delaminating on the gear case, not flowing smoothly to the prop. That speed is different for every boat, drive height, trim angle, their are many variables. The nose cone can help the water flow in a case like that. You may see 3-5 mph with setup and props, depending on what shape your props are in now