Kevin:

You wouldn't have to stock two types of kits. Stock the kits and wood bundles separately. If someone wants the full kit, throw a bundle of wood in with the kit when you ship it. You could even look at the wood bundle as an item you don't need to make much profit on, but as an extra convenience for customers to help you sell more kits. Make sure to offer the right density of wood for where used in the kit and advertise as such. A lot of guys (new to the hobby) don't know what density to use where and this would be a real plus for them.

This is only one viewpoint. You are right that in actual experience, things don't always work out as one thinks they would.