Why not HAM it up instead/in addition?
Could always consider getting your HAM radio license. It's good for 10 years and equal in permitting use of a scanner in a vehicle. Plus it's not a bad idea to be able to communicate with other HAMs in the event of a disaster, even if you use it for nothing else. During the last blackout HAMs were on the air like crazy, helping out hospitals and everything else.
Additionally I've noticed several (if not most) states have a clause allowing for a scanner in a vehicle if you have a HAM license. Whereas the Michigan permit is only good in Michigan. I have both, got the Michigan permit probably 9-10 years ago. Most people that are smart enough to operate a scanner (especially the new ones where you have to understand trunking etc..) should have no problem passing the Technician level test.
As a side note and just a matter of opinion, I would think a police officer would look less "suspiciously" on someone with a scanner in the car, who had a HAM radio license than they would someone who had ONLY a scanner license. Granted they both allow for what we're doing, but the mood/assumptions/opinion the police officer has of you during a traffic stop can have a HUGE outcome on the result.
Matt