I skipped work and took Metro North up today to walk over the bridge and I can't rave enough about it. What a great reuse of an abandoned asset, so far beyond the usual Ye Olde Historical District full of frozen yogurt shops. On a cold windy weekday the bridge was swarming with people, looked like locals mostly, just out for a walk, jog or bikeride, but some tourists as well.
My only quibbles are that it doesn't have much of a railroad-y feel with the concrete walkway and galvanized railings, unlike the High Line in Manhattan but I'm not complaining.
I explored a little at each end and while there's no formal rail trail yet they are extending the west side and plan to do so in the other direction.
A great day trip from NYC and this might be something that non rail nuts in your party would go for...amazing views, hawks circling overhead...an awesome civic asset and railfan magnet.....John