Sorry for the delay in getting back to you. 

Don't bother to add SHAPE@ to the fields list like that; it's already the first entry in the fieldslist.

Unfortunately, I don't really have a good answer for you.

If it works for you, your original approach of just comparing shape will work fine. You can do this either with a cursor, or select by location where they're identical and invert the spatial relationship. (There is a difference of one record between comparing via cursor and select by location. I'm not sure which one it is, and I'm not sure why).

I don't know your data as well as you do, so it isn't clear to me what differences are acceptable. It might be most time-efficient to add the missing records based on shape and then manually reviewing (FindIndentical is a lifesaver)