With proper ambassador and spy perks you can achieve 100% success in 1 month missions to steal research. If you encounter ancient empire with advanced tech - you can literally get 5 new technologies per month for free.
1. Default difficulty for research stealing should be increased for all empires
2. Research stealing difficulty should correspond to tech level. 60k research tech should not be same difficulty as 300
3. Research stealing difficulty for old empires should have extra boost
4. Research stealing difficulty should be tied with diplomatic relation level, but should not change after mission was assigned. Stealing techs from +50 republican ally should be easier than stealing tech from -50 hostile hive mind.
Also there is a bug with spy automation - even with counter espionage ration set to 0% AI assigns most of spies to this activity.

