I'm not sure if someone's found this out, but there's a method to make lots of money quickly and fairly easily...but I'll leave it to you to figure it out. However, I'll give a hint:

What would happen if all the high-ranked agents were "caught"?

It's a fairly decent and easy method (requiring two VDPINs each time, but...you know...), although I'm not sure how many times this can be repeated.

I believe you were referring to the mission to rescue fellow hacker from jail. First, you must find out who the top ranking agents are (might be from other mission by accident or by doing the mole mission). Then hack into Global Criminal server, have all of them break parole and arrest them. After that, the uplink corporation will offer a job to rescue them (each payment roughly 10k). Rescue them, arrest them again, rescue again, lalala, lilili.

The only thing I'm unsure about is when you release a uplink character from jail and when you take/complete the mission: does that improve or lower your neuromancer rating?

It doesn't appear to affect it much...although I'm not sure how much it drops because my rating is currently "Morally Bankrupt"

No matter what, my neuromancer rating always ends up at "Morally Bankrupt"

That's because you take missions which target individuals instead of whole companies. The latter "improves" your neuromancer rating.

Story of my life!