I've changed hundreds of clutches without surfacing the flywheel. Often it is just a waste of time and money. The flywheel should always be inspected carefully and if in doubt, it is wise to resurface it.
Make sure that it is resurfaced by someone that knows what they are doing, especially if the flywheel is a "stepped" flywheel. The relationship between the "steps" is critical. If it is done improperly it is worse than not surfacing it.
