You don't have to rename anything.

The .spc files are the "original" files that you find along with the maps, they contain only fixed speed cameras, traffic lights, and average speedcam, but only on the most important roads.

With .txt files you can have more categories and coordinates.
The program does not read the .txt files directly, processes them and forms the speedcam.spdb file, this is the file that the program reads.
The .spc files are read directly by the program and if they are alone, (without any .txt file), they do not generate any speedcam.spdb file.

If no "speedcam" type appears on the screen, either because they are not there, or because you have not activated their vision, (generally by default they are disabled).

Try opening a .txt file with Spudigo, look where there is a high concentration of speedcam and try to make the demo in that street, you will not have the warnings, but the icons on the route must appear anyway.

You can find the Spudigo program here:

[Only registered and activated users can see links. ]