I have some resource bonuses hero powers etc tied to anomalies - do I get the bonuses for planets that have explored anomalies on them or only those that are not yet explored? Interesting if a little frustrating if the latter - giving you an incentive to retain an air of mystery about your own planets!

It's the number of explored anomalies, not yet-to-be-explored curiosities.

Ah sorry I got the two confused. Is there an easy way to get an overview of the systems with anomalies or do you just have to page through your system screens?

I think you should check it system by system. Empire Overview screen (F1) could be helpful.