I'd say "average" judging from my visit in Portland. There was very little advertising, mostly word-of-mouth, but Portland seems to have a fairly large closet railfan base and other events that have had similarly little advertising had much larger turnouts (even during working weekdays). I'd say I saw as many or more people at the Columbia Gorge Model Railroad Club's open house (first day was yesterday).

No line to get to the train, was easy to get pictures of the locomotives. Inside a fair amount of people but definitely had space to move about and time to take pictures inside and look at the displays. Inside the station a few more people looking at the various booths set up, but again room to walk. Definitely NOWHERE near National Train Day when the place was a zoo. Actually, WORSE than a zoo.

One of the big differences is that the Amtrak 40th Anniversary Train is not really geared towards the families-with-children. Heck, I'm 34 and I have no personal experience of the pre-Amtrak passenger train environment, or the events that led up to Amtrak. Why would my seven year old son care? He was mostly interested in the HO scale models throughout the train than anything else (well, except the whistle display and the yard signal. But strangely he could have cared less about the locomotive control stand.)