Can't say I've noticed any great change in fuel consumption.
Recently covered 30 mile trip out to Ailsa Craig and back. I filled the tank up upon return and found I had burned just over 5 litres. I don't believe I would have burned any more less when it was a 15hp unit.
I tend to do a lot of trolling when I'm out fishing.
When out exploring I tend to get on the plane and throttle back down - maintaining the minimum amount of revs to maintain planing. I don't like revving the guts out of it for prolonged periods.
The engine now noticeably revs higher at WOT under load, it spins up a bit quicker when getting on the plane now too.
In my opinion it's worth doing.
I ordered a new gasket set with the carb. My mate who is a mechanic kept me right when doing the upgrade.