I also have a 1980 C 30. My P.O. installed a large bimini which is great for keeping the sun off your head, but it can rub through the bimini canvas from the boom rubbing on it. My P.O. removed the boom & raised the steel plate which attaches the goosneck to the mast in the mast track slot. There are 4 screws which hold the gooseneck to this plate. To raise the boom permamently you have to drill, tap & thread new screw holes for the gooseneck to be raised. My boom has been raise approximately 3" to allow for standing headroom under the bimini while in the cockpit. You can then raise the main higher up to the top of the mast as you described, so you can still fully hoist the main sail. The downside is it is a P.I.T.A. to remove the mainsail from the mast, as the slot for the sail slugs cannot be accessed without first removing the boom from the gooseneck. This requires some juggling to remove & reinstall the mainsail at the beginning & end of the season. (I just went through this arduous procedure). Also, when you raise the main 3 inches or more you are raising the center of effort / wind effect on the main, which can cause more heeling force on the boat. I have noticed that my C 30 is a lil' more tender at high winds then I would have expected with its heavy displacement to length ratio.
Lastly, I would not recommend only raising the topping lift to give extra clearance of the boom over the bimini. This will cause only the end of the boom to be raised & can cause the main to become baggy at the foot of the sail, & hurt performance as it will be much harder to flatten out the mainsail.
My 2 cents.
