I am not an airline employee, but I have friends who work for Delta and I was a holder of one of their companion passes between 2009-2012, so I have flown alot of non rev in my time. In my case, it really got me hooked on travel, and it allowed me to both fly in business class frequently as well as afford travel at a time in my life when I did not have much money at all (grad school). I have applied for jobs in the past (didnt land any) and I know exactly how you feel. That said, I would offer the following caveats:
1) I have noticed as a previous poster eluded to, space is not what it used to be. I fly now on confirmed tickets, but I still check the monitors esp when flying DAL to harken back to the good old days. It used to be, during the recession there would be plenty of open seats pretty much everywhere if you were willing to be a bit flexible, including in business/first. Within the last few years I have not been seeing nearly the openings I used to in all classes. Granted, I dont have access to the system anymore so I cannot say thats true on all flights, but thats the power of observation. I wouldnt necessarily count on being able to use those bennies as you might have been able to in the past. I notice my friends are traveling alot less than they used to. Might be due to life circumstances but I think lack of seats are a factor.
2) You probably have noticed most airlines are moving toward tiered pricing structures, and in my experience they are also selling more and more first class upgrades at check in. This will reduce your chances of snagging a premium class seat. Since you identified the chance to fly J and F as a consideration I am pointing that out.
3) Keep Seniority in mind. With 1 and 2 being in play, you will be at the bottom of the employee list (but above any companion and buddy passes) when you start out.
4) Many airlines are consolidating routes. I know DAL is cancelling alot of their Asia flights. I am not sure what other airlines policies are, but its not a given employees can jump non rev on other airlines for free. I know its been done (cant do that at all with a companion pass) but Im not sure what strings were pulled.