[MoparCharlie]

Well if it's a 2 stroke engine any comparison to a car is like comparing apples and oranges.Burnt oil leaves debris that is not found in automobile engines,unless they are pushing blue smoke out the exhaust.
If it's a 4 stroke engine a comparrison could be made.Undoubtedly a boat motor gets pushed way harder than its automotive counterpart.For the most part automobile engines live in the 2000-2500 rpm range while the boat engine usually lives in the 3500-4200 rpm range.Boats are much tougher on parts.That said I go along with the others in saying that if you are going to remove the spark plugs for the minimal cost of new ones it's cheap piece of mind to just replace them.If you are hell bent on cleaning them,an auto parts store will sell you a spark plug cleaner tool.It's basically a very small sandblaster that hooks up to a compressed air line.Be sure to clean all the debris out with carb and choke cleaner.