I don’t think general principles are of much use in typography that targets specific demographic groups with specific information.

In marketing, which has been doing this for at least a century (i.e. since Starch), focus groups and split runs have been found to be most effective.

Now we have agile design, which is a more sophisticated version of such methods.

So I would say, by all means be open-minded and try unusual spacing, if designing typography for a dyslexic audience of one kind or another, but test it against other options.