Thats a lot of cash you are wanting to spend.
Personally for a car thats only done a small amount of miles over the 8 year ownership I would stick a smaller shim in it to get it within tolerance. This would then give you a measurement of how much the valve seat has worn if at all (it could have been like that from the factory, mistakes do get made and it may just be touching and no more) From there you could then decide whether its worth stripping the head to fix the valve seat or run it for a few thousand miles and have the clearances checked to see if it is closing up again.
Personally for a car thats only done a small amount of miles over the 8 year ownership I would stick a smaller shim in it to get it within tolerance. This would then give you a measurement of how much the valve seat has worn if at all (it could have been like that from the factory, mistakes do get made and it may just be touching and no more) From there you could then decide whether its worth stripping the head to fix the valve seat or run it for a few thousand miles and have the clearances checked to see if it is closing up again.