Hmm, dunno about creating entirely new resources. The ones that exist have issues though; I took a look at spawn mechanics and each one is different.
You can alter the spawn rate through the MapSetupDefs.xml file, and I've had a go at rebalancing them a bit here:
https://forums.galciv3.com/467186/page/1/#3563270
The AI currently can't use Strategic Resources (except for Tiny ships and on planets) until the Age of Ascension because of some coding errors in ComponentClassDefs.xml
I've fixed those issues here: https://forums.galciv3.com/467065/page/1/#3562130
If you want to get the AI to use some new strategic resource you've created, all you have to do is give them a blueprint to do so.