I have an '07 Signature Noble III 45', I can't tell you what the differences are between year models but I can tell you about the '07. There are loads of gadgets & gizmos on it which translates to a higher maintenance cost. I purchased mine in April knowing it needed many minor things repaired. I'm north of $7000 in parts and who knows how many hours of my free labor. The gig list is very small now and we have spent about a month travelling in it.
Wow, what a nice house on wheels it is! At 50,000 lbs. it is a great ride, especially with the air ride seats up front. Living in it is very, very nice. I'm not sure what all Monaco did to justify a sticker price of $650,000 but the end result is a very comfortable coach that is available on the used market at a very reasonable cost.