My family and I have taken the Auto Train several times, in both directions, and really enjoy it.  Unfortunately I cannot relate such an experience with a vanagon because we never took the van on the train.
It is not economical, nor does it really save you any time, but it sure beats driving on I-95, especially if you have little kids.  One trip we left my parent's house, who were living near Daytona at the time, got as far as the exit for I-4, and with the kids fighting and vomiting already, so we decided to quickly detour to Sanford and board the train.
Driving on I-95 is rarely a pleasant experience, and that alone makes the Auto Train worthwhile.  If the weather is bad in the winter it is worse.  And you can't have a cocktail while driving on I-95 like you can on the train.
One note of caution, the Amtrak trains seem to yield to freight often, so build in a couple of hours to your schedule for delays.
Try it and see if you like it.
Ant 
      From: Richard Golen <rgolen@HOTMAIL.COM>
 To: vanagon@GERRY.VANAGON.COM 
 Sent: Thursday, September 3, 2015 3:33 PM
 Subject: Amtrak Auto Train
   
Hi,

I'm planning a January trip to the Keys and then up to Daytona for the 24 hour race. For the return trip, I'd like to load my Westy on the Amtrak Auto Train. Has anyone on the list taken the Auto Train, and what were your your experiences?

Thanks.

Ric
87 Westy

Sent from my iPad