I replaced my stock with the JVC KD-LHX500. I ended up using a Volkswagen wiring harness and I do not notice any type of volume drop at all. I do think it sounds tighter, richer, better, but I think the stock speakers are limited. Was it worth it? Yep. I got it for $200 at overstock.com. It's not on the site anymore but comes back from time to time.

On a side note,

The silver matches perfectly. You can change the touch panels color to a very close tone with the lights in the car. There are slight bits of red light that match with the hazard light.

I have the Sirius tuner and Ipod adapter, KS-PD100. Sirius is great although there is slight bit of lag with the controls. The Ipod adapter is great in that you get great sound, however the controls are a bit quirky. It takes a bit to get used to and sometime there is such a great deal of lag in the response of the controls that you end up hitting whatever command twice since it seems that the first one didn't register. Such a mistake will end up with a hassle of selecting the wrong song or menu.

This wouldn’t be a problem on other units as the controls are easily selectable. However, with the touch screen it's hard to "feel" where you need to stick your fingers so you end up spending more time staring at the radio than looking at the road.