Speaking solely from my personal and ongoing experience, Yes, a ThM or STM can help in the quest for a doctoral spot. I tried applying to a couple doctoral programs a couple years ago, and was rejected at one and waitlisted at another. I'm wrapping up my STM thesis right now, and I have an admissions offer at at least one school. And they said that the STM made it an easier decision on their end. My MDiv numbers were in the range of yours, and my STM numbers were a bit better. Plenty of school seem to not really view an MDiv as a truly academic degree, even to the extent that some don't count it as a qualifying masters degree. A ThM or STM will fill that requirement, and will demonstrate a capacity for advanced work. The degrees are usually considered as preparatory for doctoral work and would probably open some kind of door for you if you can't get one to open this year, at least that's my experience.
A side note, I did my STM where I did my MDiv and there was considerable funding available for the degree. The STM program here also has an incredibly good (if unadvertised) track record of getting folks into doctoral programs at least somewhere.
I was sitting in the same kind of spot as you two years ago and my options were go do the STM or mentally wrap my head around the idea of never trying to pursue a PhD. At bare minimum, the ThM will give you an opportunity to do some in depth study that my be helpful in your other pursuits (I'm imagining ordination/pastorate is an option with the MDiv). So, yeah, definitely think about it.
Same sentiments as @bigsh, largely.
ThM are often treated as a cash cow for a university but if you go to one that you did your MDiv or one that has an established reputation as being a feeder school, it could work. They often have later deadlines because of the very situation you've found yourself - getting shutout from every school and now needing a Plan B.
That said, ThMs have a hit or miss reputation on these forums. If you have a particular area that you know you want to focus on (moral theology) and enough material to have an inkling of an idea for a thesis, great! If you still don't know and want to spend time poking around, avoid a ThM at all costs.
There hasn't been a lot of discussion here on ThMs and funding so I can't help much there. So while places like Yale, Duke, etc tend to offer some funding, I don't know if any routinely offer all/mostly funded post-MDiv routes. Maybe others will be able to chime in there and suggest programs!
