Oh, I thought this was a thread about making Envoys clerics .

TEC envoys are amazing for generating money...the Worthy Cause ability generates ~2 credits/s per envoy (as far as I remember). I'm not fully sure about the current version, but last I remember, you can't use Worthy Cause unless targeting a planet that is not yours. They also boost another empire's trade income and population growth rate (which boosts their econ).  Vasari Envoys boost resource extraction of another empire as well. Advent Envoys boost culture which can help them get more money from allegiance boosts...and can help you if their culture boosts the allegiance of your planets. However as far as money for you, TEC Envoys are pretty much the only ones that get you money--which makes sense.

Now envoys also lead to pacts which is another story entirely.

It generates money for the owner of the envoy. But its other ability also boosts trade for the ally, so it can do both.