Renegade, I have done everything to which you have referred (your quote "I have been told aluminum heads and a cam will increase hp, and a nozzel extension and impeller will help with the jet performance"
), at least twice, in the 18 years that I have owned my barge. If you are looking to benchmark against a similar hull, see my previous thread below regarding my 20.5' 1988 Caribbean hull, with pictures.
Happy to share more details, but if there is one general rule in my experience, airing out the hull is the only time I have spent money on a performance upgrade that actually exceeded expectations. In my case, it was a ride plate, shoe and droop. I already had the Place Diverter, and that should be the first place you should start, if not already done so.
I estimate the ride plate, shoe and droop probably gave me a 3 - 5 mph increase on the top end. The hull airs out a bunch more, and its like shifting to overdrive when you trim it out. I did get a bit of porpoise in the ride, but you can trim your way through it.
In closing, if you are paying the normal shop rate of about $90/hr, which is what I paid, you WILL have to sell a kidney for any of this stuff. I never came away for less than $4 yards when paying for a shop to do it, and unfortunately, I always paid a shop to do it. More money than time.