I always wanted a terror drome aswell
It came out when I was 1 and not yet recieving gi joes. I never wanted however, I had a ton of the old school ones, some of the best toys I think ever. In fact I digress but ive always loved IG and WH40k because you pretty much can build your own gi joes what have you.
I did however have a few of the other playsets, and while I dont have anymore, wish I did for conversions. I do have plastic bags full of loose realistic looking plastic missiles that can be repurposed easily for terrain. I feel having played with these toys as you did I may have a bit of insight on the sets.
Looking at it, I imagine either extending the thickness on the raised cobra symbols out to the front, or back, front preferably for aesthetics (imagine it as a gothic bastion with each raised cover extending out to add armor. Maybe have 2 rings of firing steps starting on the the inside top. the first ring starting at the first notch of the interior rings structure. where the parpets are low, maybe have it extended back to allow room for heavy weapon squads, where there is high cover, perhaps short and more for covered steps to the firing line. After that raise the floor up a bit and add some recesses for command areas and maybe a vox array. Lastly if the top is able to seperate from the base id consider extending it upwards.
Being as I am quite "inspired" right now, this project has got me a bit excited. I did a poorly drawn mockup to try to make what I said above more clear.
Good luck with the project lomax, I really look forward to whatever you do