Well, I've just done it (gulp).
Just back from the dealership and still buzzing, after a second test drive in a truly mint 2004 156 SW 2.4 JTD M-Jet in dark charcoal grey. Metallic black, I'd say. How could I resist? I couldn't, of course, so I've signed for it and pick it up next Friday afternoon after full service
The car looked and drove even better than I remembered it, plus it has a pristine (leather) interior, sport pack, NICE wheels, etc. Plus FSH (Alfa), new cambelt + related drive train, new turbo, 4 decent tyres... a beauty. Km equivalent of 60k miles on the clock.
Re. the ski-flap: anyone know whether Alfa produced a protective bag-style pull-out, to protect the interior, as per Audi? There's no way I'm loading wet skis into this baby, and ski-carriers are really not the most aerodynamic/aesthetic addition. Just have to brush and dry before loading, I suspect. But it'll be worth it.
The cherry on the top was the sales guy's comment:
"Now that you've confirmed you're going to buy it, I can tell you you're doing the right thing... a man came in yesterday to see it, and loved it, but had to let his wife see it before committing to it. He's coming back tomorrow, and I'll have to tell him it's sold..."
Moral: if your mind's made up, don't leave it until the weekend!
Thanks again to all the people in the group whose helpful advice proved so useful in helping me make the right decision.