There is a great aftermarket option that is completely plug and play. Optional peripherals will require running some wires, but extremely easy.
GROM devices can be found on eBay and work with the steering wheel controls. This was the first purchase I made after picking up our 2004 Quest.
You can add a 5v USB port for charging. Add a plug for iPod and a second USB port for a jump drive.
You can also add a microphone for hands free calling.
The device is roughly the size of a deck of cards and plugs into the SAT port on the back of the stereo.
In total for everything I just described, cost me $215 shipped.
I replaced all the speakers and now have a great system. I don’t listen to DVDs anymore anyway, download them all to my stick drive.
I can provide images for anyone interested.