I agree with most of what you wrote here. It does feel like a waste in a way that, say, Timelash doesn't. Seeing the sixth Doctor in contemporary London is refreshing, at least in retrospect (probably less so at the time as Davison had had a few contemporary stories, but this and the Seville bits of Two Doctors are Colin's only contemporary stories) and most of the heist stuff is done well. Like a lot of mid-eighties stories, it feels a bit like they had a good idea for an innovative story about an alien mercenary stranded on Earth and carrying out crimes as part of an escape plan and then decided they needed a lot of familiar stuff (old monsters and characters and discussion about continuity points, but also old tropes like rebels vs oppressors) making the end result feel over-familiar.