I haven't heard of the requirement to be a car club member in order to import a pre '89 before, and I've read the doco on DoI's website quite a few times (I believe you it's just a bit of a surprise to me).
In terms of bringing a car over to be track only, this is an expensive avenue. However for bringing any car over pre '89 this is definitely the best option if the window is open to road registration sometime in the future. Personal imports should only be used for cars owned overseas for more than 12 months and which are not on the SEVS register.

Either way even if you go through an importer or not, you will need 2k for "wharf fees" as mentioned. Also be prepared for any additional customs taxes and wharf fees. Importer fees are quite small in comparison when you think of how smooth the whole process is by letting them deal with it. It's just like using a solicitor to buy a house; it just makes sense to do it.

I was quoted roughly 3k to ship a car in pieces over to use as a parts car from Japan, this excluded the purchase prices and taxes, and also assumed the car would be cut in half so that it was classed as parts rather than a whole shell and go through import approval. 2.5k for the front cut alone.