Hi Chris,
That front squeak is likely the sway bar bushings - much less likely to be the strut, but it's possible. Anyway:
Wagon:
I'd go with the 'limo' front bar, simply because the 500E bar is shaped for the V8 engine, and you may run into clearance issues on a 6-cyl setup. Out back, I'd go up one size - if you have 15.0mm now, install a 16.5mm. Don't worry about the impact to SLS, there really shouldn't be any. I also wouldn't worry about messing with the springs, unless you're looking to install the full wagon Sportline setup (not cheap for a wagon - parts from Germany required!).
Diesel Sedan:
Nice car you have there - and wow, talk about low miles! I'm jealous.
The Bilstein Comforts are the softer versions designed for stock ride height, the Heavy Duty (HD's) are the firm version for stock height. Another option for stock ride height is KONI 'reds'. The Bilstein Sport, Mercedes Sportline, and KONI 'yellows' are designed for a car that's lowered approximately 1 inch. Figure out if you're going to lower the car or not, and buy the correct shocks/struts to match. Don't lower the car and use dampers designed for the stock ride height, while this may work OK, it is not optimal for performance handling. The dampers for lowered cars also have less travel, which is nice, IMO. I would go for Sportline springs all around with the Sport, Sportline, or KONI Yellow dampers. And, of course, larger sway bars too. Assuming the rubber suspension bushings are all perfect (which they may be at only 30kmi), you could leave those alone unless you're really wanting the full Sportline setup (which is great, but not that cheap, especially if you don't install the parts yourself.) Also - the strut shaft bumper for lowered/Sportline cars is shorter and firmer, I'd get a pair of those, rather than use your existing taller/softer bumpers. (See photo below.)
General tip: When selecting the Sportline spring part numbers in the EPC, I'd recommend getting the taller/stiffer ones that will not lower the car as much. This does two things - One, it lets you use thinner spring pads (the thick ones crush down over time, which is a pain if you're trying to raise the car and can't). And two, if you really want it lower, you can always cut off an inch or two from the spring (this isn't really a great thing to do but it will work). If the springs are too low/short, you can't raise it without replacing the springs again. I'm in that boat with my diesel - I have Carat lowering springs designed for the 300E, and the car sits lower than I want, even with the thickest spring pads. I have to buy stiffer/taller Sportline springs to raise it up. Oh yeah - new springs & pads take a week or two to settle in, the ride height may drop 1/4 to 1/2 inch over the first month or so. Don't get crazy making adjustments right away or the car could end up lower than you really want. (Don't ask how I know.)
Final warning: Don't attempt to swap springs without the proper Mercedes (Klann) spring compressor, or one of the off-shore copies. Rusty (800-741-5252) rents this, as does Performance Products, if you need it.
