I think I understand -- and share -- your point of view. But due to the nature of scheme people *will* inevitably try and "fix" the prefix notation again and again, so you might as well have an SFRI for it so people can at least consistenly try to make the same mistake.
I also believe it's going to end up fairly useless for actual programming, but specifically in the case of guile -- as an embedded extension language -- I can see a valid usecase. That is: people copying, pasting and minimally modifying (configuration) snippets they found somewhere, without having to think about syntax or programming.
The more familiar the syntax is to whatever mainstream language they might be fleetingly familiar with, the less apprehensive they will be about applying the extension language. They might not feel like they have to "learn scheme" to fully use the main program guile is the extension language of.