Stereo Upgrade on a budget?

Right now I have a sony cdx-250 deck and the 4 stock 6.5" sony speakers probably like 50 watt max or something, I am not sure of the model #. I want to upgrade my stereo so it sounds good, I dont care if I can hear it whale riding I just want it to sound good in the boat even when we are driving down the lake. I would really like to keep the cost under 1000 and if possible closer to 500. I have a sony 1200 watt 12" Xplod sub, a sony XM-554ZR amp (4 x 55W RMS @ 4Ohm, 4 x 65W RMS @ 2Ohm), and a sony XM2002GTW amp (200W x 2 RMS into 4 ohms) which I picked up for like $50. Are these amps and sub even worth using or should I just re sale them and buy new stuff. What would you suggest buying to fulfill my wants. (louder, clearer, deeper)