As far as the cost in training to complete MSD or DM, it's close to even, maybe MSD is a bit more, depends on the specialties you elect to take. You have nitrox, so you need 4 more. If you take specialties that help make you better/more prepared for the unforseen, in the water...like deep, wreck, navigation, night, you'll have some additional skills over the DM that can be usefull on every dive. The DM, on the other hand, gives you leadership training and skillls that MSD doesn't. To me, PADI really overinflates the "Go Pro" line of hype. Once you do your rescue classes, they really start trying to suck you into the $600 DM "be a padi professional" course. It is a good course, and you'll learn a lot, but you DO have to be affiliated with a shop to get the "KeyMan" pricing on gear perks. Also, there aren't many/any jobs available at the DM level, most shops want OW instructor at the least. They have all the DM's they can stand when the do classes and intern/apprentice them.
It's all in where you want to go in your diving future. For personal persuit, I'd go MSD and then maybe into tech if that interests you. If you want to feel like a dive Pro and have a bit of c-card status, or really see teaching/leading as where you want to go, then DM is your path. OR, you can just do Both, Everything you learn will help you sometime ...somewhere....somehow.
Anyway, food for thought....
Darlene