Thanks for all your input, guys. I've got a 95, so it'll be a throttle body off job.
Unfortunately, I think my problems may be worse than that. On the way home tonight, it sounded really rather rough on full throttle and it was accompanied by a sort of rattling which seemed to be coming from behind the instrument panel - so I'm thinking maybe exhaust manifold on the drivers side? Revving when not under load sounds OK, and it ticks over quite reasonably. If it is the exhaust manifold, then that's it...the car's off to the knackers yard!
It could still be the plenum box, or even new plugs required - I admit it's been about 12 months since I last changed them. I know that's a crime, but I've been led to believe that NGKs are good for at least that (about 10k miles).
Looking after Nickbat junior tomorrow (I mean today, crikey look at the time!), so it'll be a day of jigsaw puzzles and Cbeebies!
I'll try and take a closer look on Thursday.