Having read that speedway has always used guests I decided to check up how many the club I supported used in their formative years fifty years or so ago because, for the life of me I could only remember them booking a guest once (for a #1 riding in a World Championship round) and permission to use him was withdrawn when the opposition complained. Anyway, they used one guest all season in their first year, none at all the second year then back to one the third year. They averaged less than two a year for the twenty years I've looked back at.
So yes, guests have always been used but not in the sheer numbers they are now, culminating in the stupid situation of a 'team' turning up with five guests, one of their own riders and utilising R/R for the seventh team member.
Maybe it's the number of guests being used these days that's putting some off rather than guests per se.