If your talking about a new shape 987 Boxster S, then many people will tell you that it would give a full fat 997 S a run for it's money in terms of handling, ride and performance. Given that it's 25 grand cheaper and you can see why it's such a highly rated car. Obviously it'll be from another world compared to a 993 - much less involving, more refined, more luxurious and probably just a whole lot easier to drive and live with. Having said that Huw, what modern car is going to give you anything near the tactile treat of a 993? The Boxster is absolutely stunning - in any guise.
You'll need a long go in one before the memory of the 993 disappears, and then you'll be smitten I'm sure. The performance and cornering envelope is so much more accessible in a Boxster than in a 993 plus you have a few gig's worth of black boxes to help you out of too much trouble, while still having fun.
The running costs will be in another league as well - 20,000 miles service intervals and nothing too hideous until you are into the 40k plus bracket and talking about plug changes and the like.
Having driven many 996's and a 997 (though not a 993) I'd say that if you don't need back seats, and compared to a regular C2 or C4, the Boxster S makes more sense.