I have nothing to add to the comments above regarding the Dearborn station. I have avoided the Ann Arbor station for the past 2 years. The only reason is that the long term parking lot has been closed due to the road bridge re-construction that is about 200 ft. from the station. It was a huge mess out there for long term parking. You may want to call the Amtrak station in Ann Arbor and ask the agent if the bridge construction is completed and if the parking lot is open yet. The last time I inquired it was still closed, but that was sometime last year. The construction was a 2 or 3 year project. Other then that, it seems to be a safe area to leave a vehicle. You can get the Ann Arbor station phone number through either information or call Amtraks toll- free number (1-800-usa-rail) and ask the agent for the direct number to that station.
I always upgrade to business class, well worth the $9 each way! B)