It seems that all (recent, at least) versions of the Selphy printer series use the same paper/ink consumables. Does this mean that they share the same printer engine, and will produce photographic prints of the same quality?
I can't answer as to the internals of the Canon Selphy printers, however they all print via Dye-Sublimation process. This uses a thermal print head, with the degree of heat translating to how much ink is transferred. This is quite different that ink-jet or laser-jet.
All of the Canon Selphy printers are compatible with supplies that have been available since very early in their introduction. For example, my 15? year old Canon CP-400 uses the same supplies available today, as does the newer CP1300 printers.
All of these printers are described as 300 DPI, so my assumption is that the print quality is the same. Same ink, same paper, and same print resolution.
I would feel comfortable replacing my older printer with a newer one.