I don't know how much good some of the above mentioned methods will do. From what I've seen most are preventative, to keep heavy deposits from forming in the first place. Personally I think your idea of performing a leak down test first is the best approach. If the valves are sealing up tight I'd probably leave it alone.
Most of the engines in those type of cars suffer the same fate, too many hours in the city idling at the stop light and not enough time doing what they were designed for, running fast and hard.
BUT........All my experience over the years is with aircraft (piston and turbine) so we may be talking apples and oranges here. It is possible one of the additives out there really does scavange the deposits off the valves but I'd be worried what it's doing to the rest of the engine.

Your assessment is spot on, too many people loaf around in these cars and they get all gunked up. Anything with a 8,000 RPM redline, NEEDS to see 8,000 revs every now and again. My personal cars certainly don't suffer the same fate :evilb:

I ran a leak-down test and it's not good... 90/19 in the worst cylinder, average was 90/40.

I think the heads will have to come off and give the top end a once over. Unfortunately these heads are a royal PITA to remove and head gaskets are brutally expensive.

I'm worried with the amount of buildup that I can't properly adjust the valves even if I wanted to. My concern is if I set the clearances then blow out the deposits, they will be way to tight.

Thanks for the input guys, I was hoping someone had a miracle treatment up there sleeve :drink:

The water through the intake is an old school method that does work. I used to do it to my old high compression muscle cars with no known consequences to me. Another possibility that might make you feel safer is pouring marvel mystery oil in it like the water method. Some swear by it. ATF fluid is also another possibility. The problem with ATF is if the Ferrari as rubber valve seals and it comes in contact it could cause problems because I believe ATF fluid has seal swellers in it.

PS Nothing works better than a hard long wide open throttle run. I had an old torino GT and blew the doors off a TA 455 SD. I all but put him out of sight and backed down to let him catch up...nailed it again and he couldn't get beside me! We pulled over and chatted. He told me he though I blew my engine...I was spewing sparks....twas the carbon deposits. I hadn't had the car long and had 11/1 compression!