[dogscoff]

If you know where the enemy's intel production planets are (which you probably won't, because you can't do any intel on them, but never mind), try to conquer them with troops. That will boost your intel output while reducing theirs. Also, researching industry / computers gives you the citizen databank facilities which, if used carefully, will boost your output considerably.

A good way to guess at enemy intel worlds is to look for planets with low resource values. These are less likely to be for mining / farming/ rad extraction. If a planet seems to be producing ships then it is less likely to have intel facilities on it, and in any game which started at low tech, intel facilities are likely to be on worlds a few systems away from the homeworld, because most empires will have expanded quite a bit before they research the intel tech.