I think you should send it right before you go out of town. That way, she'll have time to think about what you wrote while you're away. Of course, I may just be saying that because I'm a big chicken about those things...
You'll also have time to look it over. I'd pray over it too...Pray for you wifes heart as she reads it, and that she'll see only good intentions in it.
That is what I am going to do, i will rework a couple things i thought of tonight.. and if you want you can help me again?
I will pray as well.. (i have a family of prayers too..)