Yes. I know. None of which seems to be popular and in use on conventions. Maybe it's because the design or maybe making board games with LEGO is not a good idea... Anyway, I'd like to try out yet another, different design. I must try that plate solution you suggested.
The 1x2 Technic pin bricks are only an option if you want to make a 6x6 tile. I want to be able to make 4x4 tiles as I find it the most optimal in terms of size. The whole game board shouldn't be too big and a 4x4 tile fits a minifig with accessories very well.
In terms of rigidness - the idea is that you won't pick up the game board. The modules should be just attached if you expand a dungeon and detach the rooms and corridors that you already explored. They don't need to be strong enough to move the whole dungeon around. It is strong enough so the modules don't detach by mistake. You can still move all of them at once if you just don't pick them up. I can imagine that pins would give up anyway in that case. The new Lion Knights castle uses clips to hold all the parts of the castle together. Also, the design I'm proposing is actually two clips per edge on a 4x4 tile. I really do think it's enough. Try to build some modules and you will see :)
Yeah, that's why I'm still holding on to the initial idea :)