$1000 to spend on suspension

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Udo,
As you are already finding out, there is a lot of steer manure on the internet posing as "Boxster Performance Upgrades". Take your money they will, make your car measurably faster... not so much. I appreciate your enthusiasm. Choose wisely.

If you are running 245/40/17 RE01Rs x 4 you are on very competitive tires for street stock. If you are not already outrunning all of the stock 996s and most of the stock 997s in Auto-X... it ain't the car.

With $1000 to spend to get the most real performance gains I would:
Lower the car 1", get a performance alignment, and remove 100lbs of weight. Maybe you will still have a little left over to take honey out to dinner.