Civ IV Best Production Choice In Specialized Cities?

When playing Civilization IV and trying to conform to the specialized cities strategy, the situation invariably arises where I have too many military units or run out of buildings that are geared towards the city's specialization (at least until new technologies are discovered). In those cases, I usually pick one of the buildings that don't necessarily belong to the specialized chain until a more appropriate building type comes along. The end result is that usually as we get towards the end of the game, most of the cities have all the buildings that can be built, and it seems like no cities are specialized at all.

My question: Is this a good strategy or does buying a barracks in an economic city or buying a factory in a military city etc... cause problems with the specialized city strategy (i.e. slower production/growth)? Is it better if I simply switch to gold, research or culture generation until an appropriate building/unit becomes available?

I'm relatively new to the game and this technique works at the lower difficulty levels, but I was wondering if it is an optimal strategy or not.

Solution 1:

Constructing a building you'll never use is a waste of production. You're much better off switching to wealth in an economic city, for example, and science in most other cases. Of course, you may decide that you're done building up and turn all cities that have enough production to have finished building specialized buildings into military cities so that you can quickly crush the rest of your opposition, thus creating cities with dual specialization. Do that only if it helps you win faster than producing straight wealth, science, or culture.

Military (i.e. production) cities should switch to science in peace time (produce a library first) to help finish the game faster if you don't want to win by wiping out everybody.

Note that a factory is a must in a military city: you want to be able to produce modern units in 1-2 turns so that you can quickly react to threats, if necessary.

Also note that if you have time to build every single building, you should work on winning more quickly before moving up difficulty levels.