First off - I need to pick a few nits with some of your assumptions - nothing personal, just being really clear.
When you say "network admin" to me that means switches, routers, hubs, firewalls, load-balancing systems, some actual systems/servers like DNS, DHCP. When I refer to file, print, database, applications servers, desktop workswtations and such, those are generally handled by sysadmins or DBAs. I realize that there's a lot of overlap out there, but when I see the terms "network" and "Microsoft" used in the same sentence, I get testy.
The second thing that gets my attention is your query about "what's the hot area right now?". There are so many hot areas it's not funny. My concern is that you're chasing the almighty dollar (or whatever currency you use) without much thought as to what lies beyond the next horizon.
I would suggest for long-term career growth, that you find something that you're good at, keep up with the field in general with some of the many free news feeds available (in case something comes up that strikes a chord within you), and concentrate on being the best possible person you can be at a chosen area.
In my case for example, I understand the mechanics of building web pages, but I don't have the artistic talent or inclination required to do a really good job of it. So I stay away from that professionally - no matter whether or not there's money in it. If you spend your time chasing money, you may advance here and there if you appear to be working in a field in which there's a scarcity of talent, but then when more serious expertise is required, unless you've worked at it steadily, you're going to be out in the cold - or at least the cool.
One of my personal pet peeves (relevant to your question, I hope) is when people ask me "How do you get into security? That must be a really hot field". When I start telling them how, they lose interest because it involves work, and learning new areas of knowledge.
There is no magic "cookie" that will instantly qualify you to make the big bucks in any area. I know of a number of frauds that seem to do well money-wise, but they depend on constant movement so that they've always got a fresh audience to whom they sound good - until the audience discovers that they're farming out the work to others and pocketing the overcharges.
Hopefully you're not that type either.
I realize that I've not given you exactly what you've asked for. Hopefully though, you've now got some serious food for thought on which to base the rest of your career.