As of now the bonuses seem too much, and the AI does nothing to gain them. I say the best fix is a combination: Make the AI attempt to get them, scale the defense universal military power + variety weapon types of defenders, and reduce the benefits (ie 15-25% bonus, 3 resource). Keeping the spawn of multiple anomalies of every type also keeps it potentially more balanced, as other players have a change to catch up and this encourages exploration.

The precursor worlds are also a great idea, but would be interesting to see more tweaking of the numbers and unique bonuses