I can already hear the muttering (yes but they should be driven and garage queens are never good) and I would agree with that. Lets say for arguments sake a 360 with 40 000 miles and a 430 with 40 000 miles. Lets assume both have been well looked after, which would be a better long term proposition from an ownership cost point of view, lets assume both F1's and both with similar clutch wear. Then say a 360 with 12000 miles versus a 35 000 mile 430, my thinking is the the 360 actually has too few miles for a 2003 car but on the other hand there may be less wear and tear items needing imminent replacing than on he 430. The converse of this would be a well maintained 430 would probably have had a few wear and tear items replace by that point. I guess I am trying to bring logic to what is really not a very logical decision.
Maintenance records for me are everything when it comes to comparisons. Mileage, not so much. And to be sure even the best kept Ferrari (be it a 360 or 430) are at best a 15 year old car and at worst in the case of the 360 a 25 year old car. That can translate to any number of things "going wrong" during long term ownership-- no matter how well maintained the car has been. I'm a visual guy. Years on any set of seats, interior panels, paint and other cosmetic items are almost always a ratio to how "new" the car is. So there's that. I bought my 360 almost 7 years ago. I looked at both the 360 and the 430, but for me the body of the 360 was the winner. The lines just appealed to me more. So I think you need to decide which car you like better first because as I pointed out earlier trying to guess the maintenance costs over the long haul is pretty much a moot point. The only advantage I can say is the 430, as you probably know, has timing chains whereas the 360 has belts. And that is a maintenance cost of about $2K to $3K every 4 or 5 years (although many here have a variety of opinions on the frequency of changing belts on the 360). Buy the car you like the best. And always leave a couple of thousand in the bank for the unforeseen.