I think C|EH would be an excellent 'primer', as you'd called it, for GPEN, OSCP and others. That said, it's still a good course for BOTH sysadmins and network engineering folks, as much of what it teaches, besides tools, is conceptual thinking, hacker mindset, and other areas which either side needs to understand, if they truly want to be security-minded in their jobs. Now, if you NEVER intend to go into the sysadmin side, then it might not be where you want to start, as you might find other certs geared more directly toward network engineering (or vice versa,) and so you have to decide where you truly want to focus.
But if you want to be well-rounded, it's a good cert to have. (Besides, a GOOD network engineer should, IMHO, have at least a grasp of what the sysadmins deal with, etc, to be effective and 'cooperative' in their working environment.) When I deal with companies and help them interview, etc, I look for rounded individuals, as those that are too focused on the network engineering or sysadmin sides, solely, tend to be difficult to work with when problems and issues arise. There's not an issue studying and working on one specific area, but I prefer the folks to be at LEAST basically studied in other technical areas. So in security, it never hurts to understand both sides of the equation.
For instance, suppose a security-based sysadmin comes to you, as a network engineer, and asks for traces or log data from your routers and switches, saying they've been experiencing what they think is a worm, or some other security risk. It helps you to understand and calm them, as you gather the data, if you have at least a basic understanding of what the worm does, and how it affects end-users, and the rest of the environment. Consequently, if you're the sysadmin, often times your network engineers don't even want to discuss their environment with you, unless you can give them data that means something in their terminology, so it helps to be open minded and again, at least a little bit cross-trained.
That's where C|EH and other certs benefit you, as they give you much more useful information and understanding of how hacking tools and things work, with relation to the overall picture. They also help to guide you in methodologies for testing your security, and to do so in a routine manner, by which you're less likely to miss things, and present a much clearer picture to those who need to see / hear it. So I'd say, it's worth your time, one way or another, if you plan to study security. As to where you put it in your priority list, that's up to you, based on your time, your other study plans, and resources available to you.
Good luck, and let us know where your studies lead!
~ hayabusa ~
"All men can see these tactics whereby I conquer, but what none can see is the strategy out of which victory is evolved." - Sun Tzu, 'The Art of War'
OSCE, OSCP , GPEN, C|EH