My second bike is a Trek 7500 Multitrack with suspension and a rack. Love it, however.........
Hybrids are the "gold" standard for rail trails. I thought I needed a hybrid also (we ride a lot on the Katy rail trail in MO). My two cents is hybrids, in general, are heavy. I've had two, just for the Katy. My sis is riding my old one, and we can't believe how much lighter my road bike is next to hers. What she really wants for rail trails is slightly heavier/knobbier tires than road tires--somewhere between 32's and 28's. And maybe she prefers the flat handle bar style and with a rack? My current Trek hybrid has full suspension, but it's HEAVY! Almost not worth it, but I used to pedal along on a cloud doing 9.0 mph, not even trying to avoid branches-I just rolled right over them on my big knobby tires!
I just trying to clarify you don't have to ride a hybrid on a rail trail (although everyone will tell you that). Hybrid and "light" and a contradiction. We ride our road bikes with 23's on the Katy (although, now I try to avoid the larger tree branches). We've worked my sister back from 35's to 28's and she was surprised that with less effort her speed increased and stability is still good.
"Well-behaved women seldom make history." --Laurel Thatcher Ulrich
'09 Trek WSD 2.1 with a Brooks B-68 saddle
'11 Trek WSD Madone 5.2 with Brooks B-17