I would say the general "rule of thumb" for tipping bellman, redcaps, etc. remains $1.00 - $2.00 per bag.

Having said that, I would not tip less than $5 for the long walk from the Acela club down to the platform, and if there were multiple bags or people, $10-$20 is appropriate. I think your past tips would be viewed by the red caps as both generous and appropriate.