As someone who loves exploring abandoned (and active) railroads as well as being active outdoors. I do find that rail trails are often the best of both worlds. While I agree that some rail trails do not give the history of the former rail line as much focus as they probably should, it does make it more fun for me, the trail user, to search for lost artifacts along the right of way.
The fact of the matter is that there are so many abandoned rail lines that probably have almost no chance whatsoever of being resurrected for rail use. Given the options of the right of way either being sold off to private parties and developers or converted to a rail trail, I would always take the rail trail hands down. Rail trails give the user the opportunity not only to get outdoors, exercise and stay in shape, but also allows them to see a piece of history that normally they may have had no idea even existed in their backyard.
A great example was recently in Bedford, MA at the end of the Minute Man Bikeway, I was pausing for a breather halfway through my ride, two women in their twenties were stretching nearby before going for a run. One said to the other that she thought it was really cool that they were about to exercise on the trail and also seemed interested in the restored Budd car and freight house. They definitely didn't fit the typical railfan profile, but at the same time, having access to the trail and history made them both more interested by default.
While it would be nice to think that someday there will be in the increased need for rail service in many areas, the fact of the matter is that there are some lines that are just simply never coming back. As someone who loves going out an exploring the remains of these rail lines, it becomes much more difficult when access has been restricted by private landowners. Look at the former Eastern route in Seabrook, NH. That power plant is now a huge obstacle to either commuter rail to Portsmouth or a trail, and as a result, the right of way is just sitting there with no one able to use it. At the very least a rail trail would let us railfans be able to explore the old right of way, and imagine what it would have been like to ride through on the train.
Another great example that could have great potential in the future is up in central NH. I recently read a report that there's talk about wanting to build a rail trail from Bristol to Hill on the remains of the Franklin and Bristol RR, abandoned in the late 1930's. There is absolutely no chance that this right of way would ever be reused for either passenger or freight service, and I had assumed there was nothing left of it in the woods. The report however, showed pictures of the former turntable site, a milepost as well as some interesting rock retaining formations. Access to the area is very challenging since there is no real road access or public ways to the old roadbed. A rail trail will open up this piece of history that has been hidden in the woods for almost 75 years.
My point is, I understand that rail trails can be much disliked n the rail fan community, but I think at the same time the provide a lot of benefits to everyone, including railfans that shouldn't be overlooked.