If you have some spare time and it's not too much trouble a "lock symmetry" check would be  cool.
It would make sure all the muscles have the same values on a symmetrical creature. =)
I'm assuming you see where i'm trying to go with this while i am waiting for my jumper to go up straight. :D

That sounds really interesting and would probably improve the behaviour of a lot of creatures but I'm going to be honest: Implementing this would be quite a lot of work so it's probably not going to happen.

To be a little more specific, parts of the code that would be affected by this would be:

• The creature building logic. I'd need to have a way to figure out which muscles are a symmetric pair. (There are a bunch of edge cases and problems that come with that)
• The creature saving logic. I'd need to add this additional information about symmetry into the save files, which would then cause me to have a new save file version which needs to be distinguished from the old ones.
• The runtime logic of how the brain connects to the muscles.
• If I implement synchronized symmetric muscles, why not just allow the user to pick arbitrary groups of muscles that will then receive the same brain outputs, instead of restricting it to symmetric designs. 

This last point is actually quite interesting and could lead to some really cool results. I'm now a little bit more tempted to do it. It's still going to be a large amount of work and is most likely not going to happen in the next year or so because I just don't have any time, but maybe with the next big update (if there will ever be one).

The nice things i want are always too much work. lol
Would  new "joints" help, you'd have two and you can use them to indicate where to split the creature, if that makes sense.
The muscles would only initially have the same values, after that, it can evolve just like it does now, it would only have a symmetrical start.
Setting muscle values manually sounds very nice but then, as you said in another thread, it's not really evolving on it's own.
Oh well, it was just a thought and i already knew it probably wasn't going to happen any time soon.