FWIW, I dove my Porsche every chance I got ...
Ouch, how'd it hold up to being submerged?
I think stuartv is still slightly missing the point; the "expensive/good" camera wasn't bought for uw photography, it's for photography on land, right?
Similarly, my previous hobby was sports cars; I didn't buy them to sit in traffic during a commute, I bought them to enjoy the exhaust note while cruising open roads with the occasional spirited driving, but to each their own of course.
Anyway, that's my understanding of your point regarding someone who does above water photography with an expensive camera that is thinking of getting into uw photography.
I never did any photography before uw photography so I didn't have the dilemma.