Pick one that you enjoy and specialise in it, buy the books, read them, do the exercises, do the certs/degree/whatever qualification is suitable for that area.
You're correct in saying that a generalist won't ever earn much, but having a good grounding in multiple disciplines already puts you in a much better position than many, and it should allow you to choose a field that is growing. This may seem unfair, but it's near impossible to learn everything to the depth required to operate it effectively in a larger scale, and this is where the money is.
The generalist will only ever exist as a filter for the specialists (i.e. 2nd line), or in a small company with small IT budget. I know this as I used to be a generalist, and tried to learn everything (Programming, SQL, Security, Networking, Windows, Linux, Telephony etc). A lot of it stuck, and it makes it easier to learn new things, but unless you do something regularly you'll never get good at it. I specialised, and I’m now 10 years later I’m earning a very good wage, with a good employer, and I’m looking to move into Architecture/Pre-Sales /Consultancy type work.
When it comes to applying for a specialist job, focus your CV so that you only really mention the parts that a relative to your chosen specialisation in detail, and be prepared to be asked the tough technical questions to prove that what you say on your CV is true. Don’t discount the rest of your experience, mention it if you think it’s relevant to the role. If you can get through the technical interview, and your CV demonstrates the experience required you are on the way to getting into your chosen career.