I don't think avenger springs in the rear, and stock springs in the front are going to be a problem. Most of the time with FWD and nose heavy cars (like ours) the front suspension is more critical than the rear.

I've driven around with my shocks at full soft in the front and full stiff in the rear (I forgot to change them back when I was at the drag strip) and the car still drove around fine.

If anything, stiffening the rear of the car would help to reduce the huge understeer we have. The ride might be a bit bouncy, but with the majority of weight over the front wheels, and with the front shocks/springs soft, it wouldn't be as bad as, say having a stiff front end and a soft rear end.