Good idea Mab, but you would have to eleborate on what is "frequently choose the same map" some people might play 5 a season, all on that map, lame, some might play that map 5 times in a Season, but play 20-30 different maps also, for me this is ok.
1st part I totally agree with btw xD
Perhaps a % would work? For example
You may use a map for 10% of your total played games, so if you do like 60 shoppers, you can use a map 6 times, 70, 7, etc.