I think the advice given here can also apply to your other posting regarding pursuing a Master's degree program. The senior DBA's who posted here all recommended more experience with a lesser significance of more credentials (certifications or degrees). If you want to move into a senior DBA position, you already have the prerequisites (Bachelor's degree and MCITP) so now you should focus on DBA experience that you can list on your resume and thoroughly explain in an interview.
However I'll also stick with my recommendation to learn other databases. You will have more opportunities for advancement if you can work in a mixed database environment versus a SQL Server-only environment.