OK, Lux, Thanks for playing along. Here's my reply.
The 240-hp engine of a 987 provides only a little less power than the S of a couple years ago. The difference is negligible.
It's not negligible. The 986 S still has significantly more torque. If you cared about top speed, then HP is a good comparision. But if you care about acceleration (as most people do), then torque rules. If you don't enjoy dropping the hammer, then why buy a sports car?
To follow your logic then, you'd want a 911, or a Corvette, but not an S. You always can point a different car to get "a little more" acceleration or speed. My point is that the basic Boxster is sufficient for its intended purpose, sporty cruising, and that the S is not worth the $10K increase.
I'm not going to take the car onto a track.
If that's a justification then a Honda Accord with 240hp would save you tons of money.
Wrong answer. I want the fun of driving the Boxster. The extra money for the S is not worth it.
I don't plan to race anyone.
So if you don't buy a sports car to drive...well, sporty, then what do you buy it for? Utility?
You're replacing logic with sarcasm, and making my point for me. I do want sporty driving, which is amply served by the base Boxster. Still waiting for any justification for $10K more for the S.
I love driving, but I'm doing 99% of it in town, up PCH or on the freeway, which is no place to try to push any limits of speed or handling.
So let's see, with more torque on the S (986 or 987), you can get to 20, 30, 40, 50, 60...etc. faster. I don't think getting to 60mph as fast as you can is "pushing the limits". But it is a lot of fun and part of owning a sports car.
But just barely faster. Not $10K faster. Not 911 faster.
Again, if you're not going to be doing any of this, then why buy a sports car in the first place? Or, why not buy a Mazdaspeed Miata with 170hp? It would be significantly cheaper than a Boxster and provide 10/10ths of what the Boxster provides if driven as you allude to.
But you're not answering my question, which is why pay $10K more for an S.
If you're going to get an S for performance, then you better get options like the Sport Chrono and PASM too.
Sport Chrono and PASM are driver aids. A person might elect out of those options because they want to improve their driving skills yet still have the fastest model of the Boxster.
Would you opt out of these options? If you're emphasis is on performance? That's inconsistent.
Once you do, the price is getting up so high that I can't imagine not just getting a Carrera coupe.
Let's see, you're comparing a fully loaded Boxster S to a stripped down Carrera hardtop? First of all, the 2 cars are obviously different. Why don't you compare a Boxster S to a 911 Cabrio? Second, mid-engine and rear-engine handle differently so how can you even compare the two?
I'm not comparing a 911 Cab because the 911 was built to be a coupe. Again, you're making my point. If you want a sporty, top-down cruiser, the base model is fine. If you want high-performance, then you want the 911 coupe.
If you want a car to race, why get a convertible anyway? If you want a convertible, then you're not really racing.
Does it say that somewhere in the Racing Handbook? Come to think of it...aren't F1, champ cars, prototypes, etc. all open cockpit cars? Weren't all the old racing Porsches open air cars? Old AC Cobras? Hmmm.
Gee, I didn't know that those purpose-built open-cockpit race cars had soft tops hidden in the back, and that they were designed to be street legal. You've gone tilt here. You may as well concede that the basic Boxster fits the purpose of the car, and the moderately higher performance of the S isn't worth the price tag.
OK, now talk me into an S, but when you're done, tell me the price of the car and why I'm not getting a new 911 coupe for $10K more.
Along with the above rebuttals, I'd have to say "why aren't you buying a lesser car than a Base Boxster?" Afterall, there are plenty of cars that are just as fast or slower that are cheaper.
Because I want a Porsche, for all the obvious reasons -- style, handling. My post stayed with comparisons in the Porsche line.
So you see, your argument doesn't lie in the Box S vs. the 911. It lies in the Box vs. the S2K, Miata, Solstice, Sky, MR2, TT, Z4, Crossfire, and 350Z Cabrio. I'd like to see you justify the Boxster against those sports cars...as well as against the Maxima, Accord, G35, Neon R/T, and RSX (to name a few) relative to how you perceive you'll drive the car.
But that's exactly where the argument lies, comparing the Porsche lineup with itself. You can't support your position without going to different makes. My point still is, if you want a convertible, get a base Boxster. If you want performance, get a 911 coupe.
And last but not least, the Box S costs more initially, but also resells for more. So the actual amount of money spent doesn't really reflect the actual cost-to-own differences.
Same argument makes you buy a 911, or a GT for that matter. Plus, I thought you recommended against PASM and Chrono -- doesn't that cut against your resale value argument.
Your turn. 
OK, I've considered your attempts at refuting my position, and the answer is clear. I'm getting an S!!! I wouldn't be getting a Boxster if I wasn't at least a little bit a thrill junkie. No damn Z4 is pulling away from me!