Well, after a second go with the contact cleaner this morning, I applied a pea-size blob of dielectric grease to the contacts this afternoon and slid it in and out a bit. Just been out for a test drive now.
Er... Wow!
This has definitely made a difference, even though there was nothing exactly "wrong" with the car before. As others have said, it's more responsive and so smooth. The turbo whistles in response to the tiniest movement of my right foot.
If you're an old-ish fart like me, you'll remember the good ol' days when you used to take your car for a service and it would get new points. It would then drive like an absolute dream. Over the next 5k miles or so it would deteriorate very gradually, but you wouldn't notice until the next service. Nowadays, cars drive exactly the same whether they've been serviced or not, but smearing the MAF connector with grease has just given my TDI that "new points" feeling.
Tomorrow I'm going to fill the socket up with grease, as suggested by various people on TDIclub, in the hope that this improvement will last.
Dare I say it - this is almost as good as the remap!