Congrats on finishing your instrument ticket! I vote yes for continuing your training. You've just knocked out arguably the hardest rating there is. Life is going to throw you curve balls either way. You want to be standing in the batters box when they come your way.
Aside from the importance and value of being a CFI, there are so many ways that a commercial ticket could benefit you. Just by getting to know people around the airport(s). It sounds like you really have your heart set on 121 flying and that's great, but it's not the only game out there. I'm sure many RJ pilots "stopped by" a King Air or something along those lines, along the way.
I say keep flying and keep advancing if you want to fly professionally. That's the only way it's ever going to happen, regardless of the current state of the 121 industry.