We use baggage trains as objectives in certain scenario's and given them a Victory points value, we toyed with the idea of giving them a basic stat line of:
1 att a range 15 missile att 1hit no armour and a max move of 10cm cannot charge or evade
this was meant to represent, the troops and camp followers left behind with the baggage, we tried it once or twice but never stuck with it, though it didnt seem unrealistic
we have also used them as an encampment and simply as scenary, all round useful is the old baggage train, mine is 10 bases long and im looking to add some different wagons/carts, there are one or two that you have posted up that are already tempting me.