"I have left both radios running all night for a week and so far have not decoded anything. "
Also make sure your computer's clock is accurate within one second. Did you hit "monitor" on WSPR and yes, USB. You didn't say where you live but I could pick up 630-meter WSPR using my dental work for an antenna. Even at high noon I can pick up one or two beacons, and 6-12 beacons once the sun's down. WSPR aside, you should see and hear various modes around 474.2 kHz. Open up your selectivity. I usually keep mine at 2.5 KHz.
I've been getting plenty of 630-meters west coast stations the past few days. I'm in Missouri.
I don't know a thing about the 7300 but are you using the correct antenna port for longwave?
Beware you'll have a gross mismatch on your IC-7300 if you try transmitting into those antennas. Might fry the transmitter. Will certainly void any warranty.