Dude, SJA is a fantastic spin-off and my kids LOVE IT. My daughter loves it as much as Doctor Who itself. And 10 half-hour episodes a year is hardly over-saturation.
The K-9 series, which pretty much pretends to be not part of the Dr. Who continuity but leaves open a door to change their mind, took like nearly three years to generate a season. Not exactly swiftly using up the Doctor's ideas, that.
Heck, K9 & Company was in 1979, for crying out loud....so techincally Dr. Who has had at least 4 spin-offs...not including tons of novels and audio-plays.