How would a petrol-engined city car that's merely comparable, let alone more cost-effective, be more interesting to drive than its diesel counterpart?
That'd depend on how one defines "interesting".
A lot of people like modern turbodiesels because they can put their foot to the floor and it'll pull fairly well with no need to bother changing gear etc and no need to hunt for the red line. Easy performance and a fairly good effort/reward balance - even people completely disinterested in driving can appreciate a car that goes quickly when they want it to.
I do think a lot of drivers who've had diesels for their last few cars would be surprised with how far petrols have come on though. Ten years ago most regular cars weren't turbocharged, now a great many are - and they all deliver that same easy-going performance but with less noise and vibration than the equivalent diesel, which could be more "interesting" for certain customers.
When it comes to small stuff,
@Factor41 may have a point - most small petrols now are much more pleasant to drive than small diesels for the reasons mentioned above. And they're almost certainly more cost-effective than diesels for people who only drive short distances - probably not much less economical, cheaper to buy in the first place, less potential for going expensively wrong a few years further down the line. And in the UK/Europe at least, less likely to be taxed to death over the next few years. With similar performance to diesels but less noise it's a no-brainer.
However... I'm not sure if that's giving the average customer too much credit. The chances of them actually finding say, a three-cylinder turbo petrol more "interesting" than the four-pot diesel they might otherwise buy (for the reasons we might - engine note, higher rev limit, less weight over the nose etc) is probably very slim indeed. I hear quite a few of the two-cylinder Fiat 500s going about these days - an "interesting" car to people like us - but are we to assume the people (usually young females) who drive them do so because it has an interesting engine, or because it was affordable, costs little to tax, and came in a lovely pastel shade?...