Work for yourself - be in charge of your own destiny.
Specialisation does bring in more income.
In my case, it is not skill set specialisation, but industry specialisation.
90% of my work is with creative industries - design, advertising, publishing, video, photography.
Like anything else you need to adapt and specialisation can make you harder to employ if your field/industry takes a downturn.
Originally I worked solely in publishing fields as I have a trade background and know the workflows involved, the industry lingo and key industry players.
The entire publishing industry has taken a massive hit in the last few years so I diversified into video and also do some work with non-profits (to scrub my soul clean!!)
I am seeing a big downturn in photography over the last few months so will probably need to adapt again.
As a side not, I am often brought into large companies as a consultant and more often than not, come to the same conclusions for workflow/processes as the internal IT, but when someone from outside recommends something, its like - WOW why didn't our guys recommend that (roll eyes).
Lastly, it may sound counter intuitive, but don't cast your net too wide.
Pick clients that match your skill sets and set realistic expectations - if the arrangement isn't working out, recommend them to a colleague/competitor and get out without souring the relationship.