ABBA Gold is one of the 10 most lasting albums in the UK chart history. It sold millions of copies and went platinum in numerous countries. That means that More Gold is a realistic extension and another album really worth buying. There are many, many ABBA compilations out there, but this is the one to buy. It is 11 years old now and contains some less known ABBA tracks and most of them were not issued as singles, but were less than available on CD at that time.
Tracks such as Summer Night City (top 10) and Angeleyes (top 10) should have made the GOLD compilation (although Angeleyes is not a great track), and tracks 3,5,11,14,18 also made the top 40.
As you already know, I Am the City was the only song that was exclusive to this compilation and that alone made this album worth buying (and BTW, the song is extraordinary).
The only irritating and unimportant tracks are Our Last Summer and So Long (for some), otherwise many groups would be jealous to have such records to their disposal.
Oh, I almost forgot to mention Eagle as a song that should have been releases as a single. Such a great track.