I did toy with the idea many years ago but didn't take it up in the end. I went to an assessment day and came away with the impression that if wasn't a immaculately printed, gallery-mounted B&W print you were at an immediate disadvantage. This was a problem as I was taking colour transparencies at the time.
That, I hasten to add, is just my personal impression and things may well have changed since.
They now accept digital images, but the criteria for format etc are quite specific.
The assessment days are worth going to, they will review submissions from as many people as they can in the time so you can get an idea of the criteria they will be using for the formal submissions. They used to run some of these in the regions, you'd need to check the website for details.
As for whether it helps in marketing, I can't say but a lot of photographers selling the efforts on local market stalls seem to have RPS qualifications or one level or another.