Terminal spying is vastly useful when you need it.  In addition to debugging EFTPSR and Kermit, I've also used it to debug SMTP and (back in the day) ringing on a DL or DH line, although there were other ways to do that.  I don't immediately remember the name of the program that grabbed stuff from BIGBUF, but I think it was in the SWSKIT.  We also used spying to provide evidence to lawyers on those (extraordinarily rare) occasions when we needed to do something legal.

I've left CTYPEEK alone for now; it's just too easy for me to fall into second system rabbit hole...

Yet, I just can't make myself feel comfortable about not knowing who else is spying on what.  To that end, I've started looking at having the ACJ hook TLINK%.  I think the code in the monitor may need some enhancements.  I had to do that for SPRIW% in order to implement a Tops-20 NICE command for non-prived users.