Funny, until you mentioned it I never noticed Countdown has longer songs, except maybe The Boston Rag which is a great mini epic. "Your Gold Teeth" is 7 minutes long and I genuinely never noticed until just now! And without putting it on I couldn't have told you which track Your Gold Teeth was or anything about what it sounded like. Like I said, a lot of their stuff tends to wash over me like one big song.
I do think the debut feels slightly different to the later ones, it feels in the vein of that late 60's early 70's California rock scene to me. As people and the lyrics seem more based around New York, but the music on that one sounds very 'California' to me.
You're right that Royal Scam has some new developments, with the funkier dancier stuff... but I don't think it worked very well. The best tracks on that album are the more typical Steely Dannish songs like Kid Charlamangne and the title track.
If you've heard the rest and dug into the solo stuff you might as well go whole hog and hear the reunion stuff as well. If nothing else you can laugh at them going full middle aged boomer.