Coming back to this thread, I realise now I've started watching The Green Death that isn't actually from the era I'm complaining about, since the TARDIS is able to leave Earth by this time. So although I'm really enjoying it so far (especially Jo and Professor Jones), it can't quite count as an honourable exception in an otherwise gloomy period. The Daemons and The Time Monster (yes, I've just checked - that's the one) can, though.