No question that Rescue Diver should be your next step. Beyond that it depends on what you want out of diving. MSD is a rating and there is nothing wrong with that, IF those specialties you aquire along the way interest you and provide addtional value. Taking a specialty just becuase it is inexpensive and puts you one card closer to MSD is a silly idea. IMO.I completed AOW and 2 specialty courses (Nitrox+Digital Photographer) and have 40 dives under my belt. Would it be better to go for Rescue Diver and get another 40-50 dives then go for DM training and skip the other 3 specialty courses? I have done 15+ deep dives and several night dives so I really don't see the value in paying $500+ to PADI to get the Master Scuba Diver rating. Rather, get another 30+ dives in, Rescue Diver and Dive Master would open more doors for me as a diver. Thoughts?
The DM program can make you more knowledgable but is not designed to make you a better diver. The primary focus is demo'ing skills, assisting and guiding. Students look at DM's and the 'fun' they have and want that, but have little insight as to what it takes to achieve it and what the 'compensation' is. Talk with the DM's at the store, get their thoughts on the stores program and instructor.
Many divers are offered the DM program because an instructor may see something in a student that they feel would make them a valuable assistant or future instructor. You need to feel the same way about assisting and instructing because students are also pushed into DM programs because that is the highest rating that particular instructor can teach or the instructor needs that one more so they can reach their next rating.
Taking the tec route after Rescue will provide addtional knowledge, add dive skills that may not have been part of any courses you had previously taken. Those combined will reduce your risk as a diver. Start with a Tec40 (PADI) or Advanced Nitrox & Deco Procedures sometimes referred to as AN/DP (TDI) or similar from other agencies.
Just my .02