I had an idea that may combine a couple of ideas. Given that you specifically want to operate or build out several of these crossings and have them activated by simple insulated rail. First build a single high current flasher, rather than individual low current flashers at each crossing. Then run a flashing bus- 2 wires that alternate power around the layout just for these crossings. Last, the trigger or return at each local crossing is the insulated rail. In other words, this flash bus power source and the outside rail common of the layout would share common. Then as the train goes around and the wheels connect the insulated rail to common- the flashers flash because the 2 flasher source bus lines are alternating.
Just like any other circuit- a relay could be used to take a low current control signal and close or open high current contacts, but the constant timed click, click, click, might drive you nuts. You either want transistors or maybe even a pair of Solid State Relays (SSR).
Again, in my mind, one could build a simple flasher source from a 555 timer, but key is then making it a high current output to alternate 2 bus lines that all the flashers connect to.
Pros:
1 flasher circuit for the entire layout
bulbs or LED can be used regardless
Cons-
the need for the bus wiring (still less work in theory than multiple flashers IMO).
The design to build a single high current flasher- and not use relays to avoid the click driving you nuts.