here are my thoughts about this:
"MAYOR OF FOO" VERSUS "MAYOR" OF "FOO"
I am in favour of a separate item for every town and village which has a mayor or a council.
I am against have a "Mayor of Foo" item for each these. If the mayor gets an item then the deputy mayor and the sheriff and the dog cacher should get items too. Much better to use the 'of' qualifier.
If an administrative division has 2 councils e.g. the Senate and the Congress in many US states then create an item for "Iowa Senate" and use the statement "office held:Senator. of:Iowa Senate" so it keeps the same pattern.
NOTABILITY
My opinion is that a separate item should be created wherever this is necessary to record statements about a concept. If there are no useful statements you can make about it then it probably doesn't need an item.
Example 1: The "Iowa Senate" has a foundation date, a quantity of members, a headquarters location. "Iowa Senator" is a subclass of "Senator" and there is not much more you can say. (Note that even on the English Wikipedia "US Senator" is a redirect to "US Senate". Only the Occitan wikipedia has separate items for these. See Q13217683)
Example 2: If we want to record the overall results (votes and seats won by each party) for the 2014 elections to the Iowa senate then we will need an item for "2014 Senate elections in Iowa".
Example 3: If we want to record the results for each constituency the we will need an item for "2014 elections in North Iowa Senate district" and for all the other electoral districts (but I hope we can come up with something so we don't have to create an item for all the failed candidates).
That is what I think.
Joe