I'm not a big fan of the 'guest spot' on Strictly; it's usually my cue to go and put the kettle on.
I know Strictly is more an entertainment show than a dance show but, for me, the only 'entertaining' guest last series was Paloma Faith, since she was the only singer to put her ego to one side so that we could concentrate on the dancing. Admittedly, her appearance in the final was accompanied by all the eliminated couples, so the cameras concentrated on them rather than the singer, but that was fine by me - if only all guest appearances worked that way!
Another guest (can't remember who

) had an ego so huge that no dancers accompanied the performance (weren't there a lot of candles on the dance-floor or something?). Again, that's fine by me - either pure singing or pure dancing, but not the compromise of not being really able to concentrate on them both at the same time.
I'm sure there must have been some younger guests during the last series (maybe I was making a cup of tea and missed it), but there did seem to be an awful lot of, erm, well, OLDER performers. Friends of Brucie? Frankly (and I say this as somebody who is not exactly a spring chicken), a bit past their sell-by date and rather boring. I mean, I like Bette Midler, but I really don't need to hear 'Wind Beneath My Wings' or 'The Rose' yet again...
Oh, and I totally agree with katie_p - a strict quota for rumbas!