+1 on the leave it alone, but I think you already knew that.DO NOT replace any other components!
If you want a pickup cover..buy one. You may even be able to find a 70's one if you are patient. Otherwise, get a new one and you can probably "age" it your self. But DON'T replace knobs, pickguards, etc. That is what gives your bass character!
-1 on buying a vintage cover. The new ones are exactly the same as the olds ones.
Use some circuit board etching acid and some dirt to age it.
but they are almost a matched set visually and Im sorry, that Squier is just awesome!! And if I let the [backup] Cowpoke go I could keep the VMJ...maybe with a lil sweet talking to the BF Mmmmm 
with the rosewood. But the headstock is still maple and for some reason it throws it off somehow and I found my black bass loving self kind of turned off by it
White basses are cool. I won't go out of my way to get one but if a bass I want happens to be white, its fine too ^_^