I was wondering why vanilla didn't have this already. It makes sense, in my eyes.
Honestly, I feel like combined versions should get at least a small boost to one stat or another.

In terms of graphics, are you planning on making some flashy graphics for them?
I read you plan on having tanks be connected too. It would be great if 2x2 tanks would visually turn into a singular, larger tank.

I was thinking about doing that. When doubling the radius of a circle it becomes 4x the area, so it would make sense physically. The only problem is that the pipe ports would look funny and require messing with. I'll definitely toy around with things in this regard.