Interesting conundrum. IMHO, given that you didn't pay a lot of money for the car and it has done mostly motorway miles previously from what you gather, it will become a lot more fun to drive once remapped. Just give it a thorough once over to see if any parts need replacing as like FOCA said, the remap will probably put more stress on engine components.
Another option to consider would be to get a good tuning box. I know everyone has a different opinion about them, but from my personal experience, they can be a lot more versatile than a remap e.g you can turn the power down/up if needed pick which part of the rev range you want the extra ooomph to kick in. Also, with the 1.8 tdci engine, you can fit it a lot more easier than the 1.6 and can take it out,if required, very easily.
This would be something I would consider:
+1 for all the other supporting mods that FOCA mentioned as well