hey man. welcome.
ignore all the above.
caps are not bad things. just not worth buying. if you have one. by all means use it as it acts as a voltage regulator for your amp. but it does not help your cars electrical system, and your alternator will still have undue stress put on it. by upgrading your battery to chassis, alternator to battery, and engine to chassis, the resistivity of the ground plane will go down, and your battery should charge faster.
but. you still need to upgrade your alternator.
anyway. you will get a lot of hate on this website because you run JL. JL is taboo here. imo - they arent worth the money, but they have quality products, albiet overpriced.
as far as getting better sound quality, scoop a 4 channel amp and hook it to your front\rear speakers. then, if you have not already, dump your front speakers and get some component speakers. and dump the rear speakers, and maybe put some coaxials back there, and fade your stereo to the front.
thats my 2 cents.
welcome to caraudio.com