You might want to consider changing your mindset from:
"What skills should a senior focus on to make him/her self more employable?"
"What skills should a senior focus on to make sure he/she gets the job he/she WANTS?"
I've spent the last week interviewing applicants and one thing that stood out during the period was how LITTLE of them knew what they wanted. Most just wanted to get a programming job ASAP and ANY type of programming job would do.........
None of them stood out except for the very few ( 1.5 out of 12 ) and non coincidentally, they were the ones that knew EXACTLY what they wanted to do.
It's really hard not to be impressed by someone who knows what he wants to do (hopefully it's in line with what your company is doing) because the resume reflects that clarity.
He made it clear that he:
- Only wanted to do Web development. No winforms.
- Had done 3 projects, all with the same stack of tools/languages.
Did we have winform apps? Sure we did. Did we have PHP stuff? Java stuff? Sure.
BUT our main focus was on the Microsoft stack (Customer requirements but that's another story for another day...) and we knew he would fit in quickly.
The last thing I wanted to see was another applicant with 5 different/diverse languages that would/could/wanted to do EVERYTHING and ANYTHING. I swear nothing scares us more than those cos then its really nothing but roulette with human bouncing balls.
At the end of the day, I want to hire someone that really WANTS to do the stuff that he'll be doing, in an industry where turnover is thru the roof, their happiness translates to a longer lasting relationship.
Sure, you won't be very flexible. You also won't appeal to the companies who are from the other camp.
But if its not something you want to do anyway, whats the loss? :P
Aim to get the job you WANT and focus your attention on those specific areas. It will be more enjoyable for both you and the company that you end up with.