You might want to check out some of the Amtrak discussion boards. I think you will find more feedback over there.
With that said, train travel is a journey. It is an experience. I think if you go into it with the that mind set it will help alot. It is going to be lot longer and more expensive that driving or flying. I would not plan anything for your arrival day. The train is going to be late. Sometimes can be many hours late.
Since you are traveling that MI, I believe you will be taking the new Floridian route. That is a long ride. It is two nights. If the budget allows I do a sleeper car. I wouldn't want to go coach that long.
Yeah if it’s the new “Floridian” route bundle, it’s a little circuitous. Plus from MI I think you’d need to drive to IN or OH to get on it (or take train towards Chicago then switch over).
I do love train travel, but for MI to FL it doesn’t seem nearly as quick or convenient or cheap as flying…
Never used Amtrak but was curious and checked their website. Chosen random future dates and apparently it takes 48 hrs to get from Detroit to Orlando (via Chicago). Price comparisons depend on which option you choose, but I wouldn't recommend only being able to sit for that long of a ride. Seems you need to sleep somewhere or would be exhausted/sore by the time you arrive. Using up 4 days of your Disney vacation in transit seems like a very long time to me compared to an option like flying.