[Flux]

Say they had used the Paul Farrer theme (or similar) from 2008, would this revival have been as successful?

I think so. Its success is down to much more than just nostalgia, and even the (perfectly pitched) nostalgia is down to much more than just the theme. Had they approached it like Sky did and repackaged the whole thing, it wouldn't have been as successful; but IMHO there's enough nostalgia, campness and understanding of what made the first run successful in the approach that it would have still succeeded no matter the theme tune.