City influence

Currently a city's influence is based 100% on culture. This in my view can be improved by allowing a mix of factors.
The following is a small list of potential canditates:

• Overall culture
• Culture for last N turns
• Avg military presence for last N turns
• City age
• No. turns current owner had city (has the city just been captured?)
• City size
• City production of food/shields/gold etc.
• City buildings present
• Infrastructure
• Happy/unhappy citizens

The 'official' setup would be set by the game developers, but of course could be changed in a mod.
So a large city with no cultural buildings (e.g. just captured) would still have a level of influence.
Larger level of influence would of course expand the city's borders.

that's too many factor, don't you think it will take too much system resource away from other more critical calculation?