I just ran the numbers today Ian - so your question is perfectly timed. I wasn't able to get a definitive answer from Kaplhenke on where the stock roll centre is located, but given it's a strut suspension, I'm going to say that it's pretty low. I will be doing some measurements when I get a second. I found this diagram online that explains it fairly well.

Moving the LCA balljoint down moves the roll centre up a lot. Without proper data on the 240, all you have is a best guess. So this was the simulation that I did for what I'm guessing I've got. My guess is that the roll centre (I know, I now have to hand in my "Scientist" pin and rip up my PhD), would be around 5 cm off the ground (while not low, my car is lower than stock and the LCA is inclined towards the middle of the car...it's not level). With the roll correctors I would expect it to come up a reasonable amount (whatever that is...for sake of argument, I used 15 cm).
So with all the suspension information that I have, I input the values and played around with the front roll centre height. Here's what I found.
If we consider that total weight transfer is comprised of transfers that are going through the springs/bars and those that are going through the roll centre, then we find that for the current set up, the total weight transfer on the front is estimated at 380 lbs with 312 of that being handled by the springs and 50 going through the roll centre. That's 82%. So much of the work is being done by the springs/bars. The rear of the car has a much higher roll centre and as a consequence, the rear springs/bars would only see 33% of the weight transfer.
Now for the guestimate. For each inch that we raise the front roll centre off the ground (there is no moving the rear RC), we're moving the weight transfer about 5%. So I'd say it's worth the effort/money even on a moderately lowered car or maybe even a stock height car. No one can say because we don't have numbers to crunch.
One other issue that my car has at the moment is the front natural frequencies are a little too far away from the rears with the fronts at 1.83 hz and the rears at 2.2 hz. There should be 0.2 to 0.3 hz worth of difference. So a 325 lb spring would be a little better.