I'd say the 460 system is okay, you can upgrade the woofers in the front doors, and the rears, which helps. Also the head unit can be changed for an after market one that is Double DIN size to fit the hole.
I changed mine with a JVC one that I bought at Cruickshanks.com and with it purchased an adapter harness that was fairly easily wired to the new unit so it plugged right into the original Mach 460 harness. Doing it this way the original amps, which are decent, are still running the show, and trust me, you really don't want to start messing with the wiring. After the head unit, the wiring does a unique way of connecting the amps and speakers throughout the car, and should be left alone.
I'm able to re-install the original Mach 460 head unit when I sell the car, if the owner wants it back to stock.
Another thing, the truth is, how much you gonna listen to music anyway? I'm usually listening to the engine talking and howlin'. Well, I guess on the highway, to drown out the exhaust drone.....