I have been finding on newer heads that they leak down (particularly the Intake) significantly after a little running and then need to be touched up. After that they seem to to hold their seal.
Are you speaking of 206's or all heads in general?I'm sorry but i have not found that to be true.
If the head is prepared (done) properly they last a long time. I like to see the head raced at least 10 race days including practice time before it is what i would call seasoned. The more the better! I have found that if seasoned properly and then refreshed they can last a complete race season before being refreshed again. They may last longer than that but if you get it done during your off season then you know you have the best stuff for the start of the next season.
For a very large portion of the racing population removing and replacing the head on their engine is a monumental task. They may be the best driver but when it comes to replacing the head all the technical things that go along with it that simply isn't something they are equipped to do!
One of those critical things is is getting the valve clearance set properly.
I will be going to the CKNA finals in New Castle next week end and i will have large number of customers and engines there and i can promise you i won't be taking any heads off.