Yes, the City Navigator is the "normal" map for onroad navigation.
Take a look here: There you can see the Europe Version.
The Topo Maps are interessting for offroad, walking, biking ect.
And there are some maps from other companys than Garmin. The AdriaRoute for example for former Yugoslavia.
The Software: from time to time Garmin release a new firmware. Sometimes you have some new features, but most time it is "just" to correct some bugs.
It is not like WinWord97, Winword200, Winword 2003 ect. where you get dozens of new features wich every new version.
Yes, you can install every map on a current Nüvi.