To put in a simple way, your experience should equal to the value addition you do to your company.
shirley,
You have put it clearly! The customer should be satisfied with the value you bring on to the table, for the money they pay for you. In many cases, the "profit" for customers and employers is more with not-so-senior analysts. And as the experience grows, this balance (value/cost) can be difficult to attain.
This is not only for ABAP but for all modules (functional included)...
Even if you don't want to study something new because you will be amidst "younger crowds", you need to keep gathering. Bottom line is that the customer (employer) should feel more satisfied with you than some one with lesser experience, only then you will stay employed.
What you should learn...that is up to you, your liking and capacity...it can be several things like Jelena techno-(business awareness)functional 
or like Rahael says HANA etc. etc.
I can give some examples about Typewriter. I am concentrating on functionalities I have not worked on like rebates, ATP all this is in SD itself. So I choose to stay in SD and keep learning "new" things and revising topics in which I have worked.
In every meeting with customer (business or project manager) I try to add value - by doing a good job, asking questions, that showcases my experience, be self-sufficient, making the end user feel that his/her exact requirements are gathered and addressed (with clear communication).
So bottom line, we can stay in the same module as analyst for a life time, but need to keep giving more and more value, handling complex tasks (design etc.). Shifting from doing the easy to concentrating on doing the difficult. Have the belief that you can stay in the same module throughout your professional life...may be you would have to change organizations (a few times).
TW