caps are almost useless. I have used them before and they did almost nothing. If you ever need an electrical upgrade you might as well do it right by either upgrading you battery(to like XS Power, Kinetik, Shurukin, etc) or upgrade your alternator to a high output one.
If you going to run 500 watts rms you don't need electrical upgrades, I didn't do anything until about 1800 rms because that is when my voltage would drop. If it's under ~1300rms you don't really need electrical upgrades but if you go more than that look into it.