I would be totally open dating an MtF as well, or even an FtM as I'm sort-of bisexual (say... Kinsey 2) (it's a bit complicated, actually, I'm attracted to both genders physically and emotionally, but would never-ever want to have sex with a man in the 'normal' man-way. If that makes any sense)
I mainly want a partner that fits with me -mentally- and it would of course be nice if she/he was attractive as well, but it's not a must or a breaking-point. And I'd rather have an ugly wife who is 'on the same wavelength' as I do, than a hot chick who isn't.
But I agree yea, I think two transpeople will understand the difficulties of being trans better than a cis-trans couple, and will probably even have a deeper connection than most cis couples.