Good questions, but "adding god" simply means you're recognizing a cause -- the value it adds is that now you see that there is a purpose to life and to the Universe...it in no way devalues learning about it.
The value is purpose, which is ultimately what mankind searches for.
For example, you'd value a gift more knowing your wife gave it to you than you would if you found it in a gutter. Orgins matter.
The recognition of such a cause may provide certain things, but this recognition is a faith based recognition, which I do believe you mentioned in a prior post, so you are aware of that. You also mentioned that such a recognition shouldn't be in a science class since science, by its nature, can't deal with things that are undetectable unless they can be relevant in some indirect way where science suggests that they should be there, something like the Higgs Boson.
I speculate about god often because I really enjoy speculating. I think its fun and exciting. The problem is that most of the time people find no value in my speculations because they are just speculations, and I wouldn't expect people to attempt to teach others about my speculations in a different kind of class.
I don't see anything wrong at all with schools "teaching" or offering a class on intelligent design. I think if people want that then they should do it, but it can be its own class where people can speculate all they want about the subject in a structured way and the class can be like a philosophy/science-ish class or something. I'm sure others will disagree, but if the class is offered in a stand alone flavor then you can take it or not but it shouldn't be mixed in with dedicated science class and shouldn't be incorporated into science texts since it is not based on objective evidence.
Why can't it just be included in religious studies?