There is a railfan platform as you describe near me in Fairport, New York on the CSX former New York Central "Water Level Route."
The cycle time from initial idea to execution is probably best measured in years. There is a scanner there which broadcasts except at night, and a webcam in each direction recently installed by "Virtual Railfan" (recently is relative because I am not good with dates). There is a full size signal mast there now. But there are no, ahem, "facilities." The platform also sees non-railfan use from time to time.
The overall impact is probably mixed.
Some railfans don't like it because their previous gathering spot, on private property, was closed off and gated shut. (There is still a way to sneak in.) They won't come to the platform because they don't like sharing it with families and other visitors, you know, "commoners." So they've moved on to one of several undisclosed locations away from town. And I mean "undisclosed" as in they would not tell me where, just "up the track." I guess I don't know the secret handshake.
On the other hand, there is some incremental interest from those families and other more casual observers who don't know the symbol of the train that just went by, and don't care much either-- but perhaps they might become more typical railfans, which I think should be encouraged. (We were all new to this once... ahem.) Fairport already has an established 'downtown' just a short walk away; and there are businesses on the same block and across the street. And it's also just off a bike route as well, and the Erie Canal is within sight.
Is it bringing in a lot more revenue for the local restaurants and shops? Hard to say, but I doubt it. It is giving local people another reason to visit or stay a little longer. But I don't see it ever having the impact of, say, Folkston or Rochelle, that is, people traveling from far and wide to come to Fairport.
George in Rochester NY
The Unofficial Micro-Trains Release Report (among other things)