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Okay, one. If she was on Gallifrey, which is possible, she's gone now and that entire event with the Time War was time-locked so it can't be revisited or altered, or I'm sure he'd go back in a heartbeat to try and save his loved ones. The only reason Dalek Caan got through for Davros was through a (plot) hole in time. xD

Two. If she's on Earth, why'd he wanna go back and see her, even if she didn't see him? It's like with meeting Sarah Jane again: Four left her behind on Earth and knew if he went back to visit, she'd be upset at him and he'd also have to say goodbye again. And that's no fun.

Besides, who wants to go back just to see someone die? Rose only did because she never knew her dad, and she didn't want him to be alone. She was still all upset, and with the way the Doctor's been going more angsty/emo in the new series, that's the last thing he needs.

One more thing: She wouldn't recognize him now. She knows about regenerations (she was in The Five Doctors) but with his newer outfits, he even blends in more.

Sorry to necro this, but this is something I've done a fair bit of research on.

First, keep in mind that the only things considered canon at this point are the classic series, the new novels and the new comics. Allthe rest are iffy until the producers say otherwise.

Note I said the comics. This is key. Why? Because in a recent one (The Forgotten) the Doctor mentions that he once used the Chameleon Arch to fool an enemy. This story apparently predates Human Nature, and apparently was meant to solve the half-human problem of the film.

Susan? besides being bloody useless (except in The Sensorites), she drops hints. In AUC we learn Susan and the Doc are from another Time and place. In TFD, Susan recognizes Gallifrey. Yup, she's his granddaughter.

I'm pretty sure in the first episode, Susan referred to Gallifrey as "Ours" (Hers and the Doctor's), and also aliens aren't allowed on Gallifrey so I think from that we can say that she is a Time Lord/Lady thing.