I tried to compare envoys in term of usefulness other than boosting relations and thus making pacts.
TEC envoy is useful to player that sends them up. It gives credit boost,raises trade for ally, and gives population reproduction boost.
Vasari envoy is useful if u want to help player. It gives resource extraction and production boost, heals planet and makes planet invulnerable for short period of time
Advent envoy helps with culture production, sacrifice himself to boosts relations and helps with planet allegiance if cultured by enemy
Now to my problem with Advent envoy:
TEC and Vasari envoys on first research help either player that sends them or ally. As for Advent envoy it only helps if planet produces culture which as with my experience doesn't happen on every planet. In addition player has to research and build culture center.
(At this point I must say that I mainly play online with teams locked)
As for second research advent envoy sacrifices himself for relations boost. If u allied u don't need relation boost other than for pacts. And when envoy is sacrificed player has to build another and send to same planet in order to maintain relations. It costs additional credits and resources.
The only thing i like is third research quell unrest. It goes to same league with what TEC and Vasari envoys do.
I think 1st and 2nd research need to be rethought as they don't go with the same pace as envoys from other races go.
Suggestion:
For first research since culture is advent thing envoy should if there is no culture center on planet produce culture which would count toward planet owner so planet produces some culture.
For second research i think sacrifice is to costly. Instead why not raise maximum relationship bonus per planet or make that maximum relationship bonus its achieved quicker in comparison with TEC or Advent.
The other way second research could be changed is that it could give planet a shield or mitigation.
Please share your thoughts.
Greg