That amp is probably as efficient as most other class AB amps. So, your
alternator won't know the difference between running a 500 watt amp at
full
tilt and running this amp at 500 watts (that is, not at full tilt). You
could keep it if you'd like, and you'd get superb performance out of it
with
a ton of headroom. But if money is an issue, you could just sell this
thing
and buy an amp that suits your needs for half the money. If you're
really
concerned about your electrical system, sell this amp and buy a class D.


How much more efficient are class D amps?

Usually you're looking at 50% efficiency for AB and 80% class D. But
quiescent current draw for class D isn't a whole lot different from AB, so
in the long run the difference may not be quite as big.

I am reaching a similiar point with
my own install. I have a 2001 Dodge Stratus with the 2.4 litre engine,
and I
already have a Fosgate 360a2 to run my front end.... I have an Autotek XS
1500.1 that I'd love to use, but I'm a bit scared of taxing my charging
system
myself. It is a class D amp, so how does that affect things? I'm
thinking of
just running it at a higher impendence (It is 1ohm mono stable), so I
don't get
too much stress on my alt. If I was to run it at 4 ohm, would I have less
to
worry about there?

Nah. Go ahead and run the low impedance load. Worst case scenario is this:
if you wanted to drop down to the amount of power you'd normally be using
with a 4 ohm load, you could just lower the gains on the amp and you'd be
down to that 4 ohm power, but you'd have a lot of headroom.