I wouldn't put an annual time limit on membership. Some people will just use the site for info, general reading. I have joined some forum sites in the past simply for info. Ford focus owners being one when We had a Focus.
Unless there are limits to data/storage then leave it. The only change I would make would possibly be an automated message to a member who had not even opened he site for. Couple of years. Perhaps they have even passed on to the car club in the sky.
