Perhaps this is worth noting?
During a war, the AI (I play at around "crippling") will almost always fight out all battles till the end by constantly producing military units until the war is resolved.
Since the AI rarely has constructors in stock, and since the AI (particularly the more aggressive ones) does not make many to begin with, this means that the AI has no constructors and makes no constructors until wars are completed.
I have found that this makes "leeching" far too easy -- by quickly making peace with at least one party, or by staying out of the way of wars, and by either producing some constructors or have 5 or 10 in stock somewhere, it is far too easy to re-claim other civ's mines once these have been destroyed in a war. In fact, once wars begin (and I am not involved or I have traded for peace), I find I can easily leave my constructors lurking near enemy mines, and once these get destroyed, I grab them. Often, however, even this is not necessary, since it can take months or years for another AI -- even those not involved in the wars -- to take notice and grab them.
Would it be conceivable for the AI to consider re-claiming mines during war with a higher percentage of resources involved?