Noticed that I can get around the warmonger penalty by letting a toll troll try to scan me, then respond with "I don't think so!" Instant reputation drop and a provoked attack. Also, if I have money to burn, I deploy several saboteurs in row. If they fail, they did their job - lowering reputation to hostile so others do not get angry when I attack. If they succeed, I fight fewer bigger ships when the response fleet clashes with mine. The saboteurs' main job is to lower reputation on demand non-violently (to evade warmonger penalty) when that is beneficial.
Minor annoyance: Market can evade getting captured (once) when a cease-fire is declared during my invasion in progress. I just try again and eat the warmonger penalty.
Victory fanfare is nice. Too bad I did not get it again if I destroy everyone after diplomatic win. My last game, I had Hegemony as ally because I was too lazy to kill them until everyone else was gone. Once the Hegemony was the only one left, I steamrolled them in a few hours.