Jeff, my thoughts are you should probably stick to the agreement, every other weekend and one night if she doesn't come up with something else you could agree with. Then make plans for the weekends she has the kids and make her act like a grownup. I don't think many parents let their parents see the kids whenever they want whenever they may feel like it. That's making life way too difficult for you and too easy for her imo.
Her email makes me want to gag. It sounds good, but if you look at her actions has she really tried to do any of this? Does she think the D is going to make other people happy? I personally think being a full-time mom is the best way for your life to count for something!!! I just think she's feeling a little guilty and is hoping you'll make her feel better. I don't think you should say anything to her that would make her feel better! Karen