IMO, if a state is going to allow 'vanity' plates, then they need to have an objective, unbiased process for identifying which varieties will be made available. Perhaps after X number of requests, or by petition or something. I can understand a state not wanting to have a thousand different varieties of plates. But there should be equal access to all viewpoints.
There are, the federal judiciary simply acts with the imperfect knowledge that they are the arbiters of state regulations.