Ground and RCAs

i'm no expert, but i'd say it was ok unless you have some super high power running through the power and ground wires.  I have the 200w basslink and I run it with my unshielded cheapo rca wires and I don't get any noise.  Of course, nice twisted pair, shielded rca cables would never hurt.  I should get some myself, but I'm too lazy to take off all my trim panels again.

You never want to run current wires near signal wires if at all possible.  In some cases it won't cause a problem, but I prefer to leave well enough alone.  Keeping you ground short is nice, bu not absolutely necesarry.  It, just like the + wire, carries current (longer length will give higher resistance thought).  I have seen people who run the ground all the way back to the battery to eliminate any kind of possible ground loop.  For lower power situations (300 Watts and down) with good RCAs you would probably be OK, but see if you can't come up with something else first.

I think either way will get you the same outcome really.  As long as you have decent RCAs it's not gonna kill you to have them near the ground wire for a foot or so; remember too that crossing the RCAs with the ground, at a 90 degree angle, will take care of any interference.

Similarly, extending the ground wire a foot or two will probably not rob you of all your power, unless of course the cables you're using are already being pushed to their current-carrying limits.

Keep in mind that a lot of this is dependent on the quality/design of your RCAs, as well as the type of amplifier you're looking to run (4-channel full frequency amp for 3-way speakers?  or mono low frequency sub amp?)