I am going to run a mini yellow top stinger battery in my evo....take a look at those..

 

+1, a "better" battery would alleviate some of your dimming headlights, but as the battery ages you will be right back to where you started. an alternator is the only thing that will flow more power to your devices at idle. someone else mentioned running a cap; that will help for certain types of bass but long consistent drumming will run the cap out pretty quick. you are right back to alternator again. sometimes dimming comes from inefficiency in your wiring too, such as too long of a ground or under sized wiring. there are lots of options and lots of reasons for your solution and problem, you just have to try something that makes sense and then continue down that path until you are satisfied. starting with the cheap stuff is usually smartest

 

yea... so new cap and bigger power wire to start... redo grounds...