As far as the 'make it lighter'.
Sorry, but I've owned these cars for 5 years. For random street driving and twisty road spirited fun, does an extra 15 pounds REALLY make a difference?
Hell, I'll get in the car and throw my laptop bag in there (that's gotta be 10 pounds plus). Or I could run my ass around the block a few times and drop 10 pounds.
Or I could only wear a Borat thong and drive barefoot because jeans, a sweatshirt and Lotus mandated Pumas weight 6 pounds.
The point? As you note, make the car yours. If we TRULY want to go around the car, there's probably a bunch of stuff we can eliminate to reduce weight. Ditch the stereo all together. Chuck the A/C. Lose the carpets. Toss the center console cover. Hell, remove the passenger seat as we are usually in these cars solo anyway.
I'm being sarcastic, but the point is that they are cars. Cars that are driven. Cars that are driven require music. Period. Yes, we all love exhaust notes. Exhaust notes for 5 minutes are awesome. Exhaust notes through a viaduct or tunnel are super duper awesome. Exhaust notes for two hour drives suck dong.
One can easily get away with upgraded the stereo to provide a nice pleasurable driving experience with out adding much weight. I put in a better head unit, better speakers and a small 8" powered sub. Probably added 5 pounds in weight total. To offset, I just went extra spicy on the curry and left that 5 pounds in the Kohler!
Oh and to the OP - I hate the baseball stitching on the sub box!
