I,d say if you got the $$ and want to spend it.Have at it.I wouldn't mind a set myself.
Definately will enhance performance,How much?All depends on which type,and the boat/set up.
If you were running 4700rpm and had the prop worked and went down to
4600 and lost 4 mph i'd be looking into the prop situation and who did the work.
Theres no reason that if you were spinning a 24 @ 4700 prior to having the prop worked on you shouldn't have been able to atleast pick up a couple hundred rpm.
I'd first find the prop that gets you to 5000rpm-5200rpm with your current set up then work on modifacations to your engine and prop from there.
You can't fix a prop issue with exhaust manifolds or headers.
Just my 02.