I have the impression that most commemorative coins restrict their commemorative designs to the reverse of the coin.
In monarchies that will indeed very often be the case. Also, in the euro area, the commemorative €2 coins have to use the common reverse, so all that is left for the theme specific design is the central part of the obverse. With collector coins, it is a little different - most Dutch pieces for example will reflect the theme in some way. Think of the Belastingdienst (2006), Manhattan (2009) or Turkey/tulip (2012) issues ...
Finland will almost always have two "theme specific" sides, with the exception of series such as Nordic Nature. In Austria and Switzerland something interesting happened: Austria went from one specific side to two in 1989 for most collector coin denominations, while Swissmint took the opposite route. Until 2004 the Swiss collector coins had two "specific" sides (although the one with the face value was usually quite sober and did not necessarily reflect the theme). Then they introduced one value side design for all future issues. Don't think they lowered the prices accordingly.

Christian