Hi Gopal
All customers need Solution Manger for their SAP setup now (well those now on ECC 5 and ECC 6 onwards). How much of Solution Manger being used by a customer will depend on their size and landscape complexity. A lot of SolMan is in the Basis area of usage but again that will depend on the client
If you have Charm experience do you have a strong understanding of managing transports and system releases? As a different career pathway, you could move away from the technical aspect and move into system and release management. This can be quite a fulfilling job to work on implementations and support to manage transports through to production. It would take a lot more general knowledge across SAP and communication with the different teams (management, test teams, prod support, etc)
With having ABAP, Solution Manager and Workflow you are getting a good all-rounder technical skill set you. If you were to choose one of them I would probably look at ABAP and Workflow. If Solution Manager, you need to diversify in the modules.
Part of your decision needs to come back to what you are good at and what interests you. Enhancing career really depends on your goals.
Regards
Colleen