With all of these new coins coming out, why would I mine a pre-mined one?

More value is zero premine coins.
a small pre-mine is always a good idea. Nice to be able to entice people to add services.
+1
on a side note
overstock taking btc as a payment

we should see a rise in btc soon
also new egg are thinking about it, they will probably will join as well
so as soon as the BatPlane hits the exchanges we will see a nice profit i hope