Re: It wasn't bad.
I see your point, but i still think they've underplayed it to a large degree.
The only real reference in DiH was when Missy said she knew where Gallifrey was. One can only assume that The Doctor went there off-camera to have a squint and found nothing. From Wiki:
"In the interim, the Doctor travels to the spacial coordinates given by Missy, only to find nothing there; Gallifrey remains lost. Some time later, Clara meets with the Doctor to tell him about Danny's fate. Assuming Danny is alive again, the Doctor interrupts her with the news that he found Gallifrey and plans to return home, wanting to spare Clara's feelings. Clara, in turn, says that she and Danny are going to settle down and resume their relationship. They bid each other goodbye."
Nothing in this series about Clara asking to see Gallifrey, given that she is still under the illusion The Doctor found it. And if I was him, I'd still be looking round for it, given that I knew it wasn't destroyed or time-locked any more. But we get none of that, presumably because The Doctor was off down The Sunglasses Hut.
Similarly, the Gallifreyan device he's carrying round is meant to be his final confession and his last will and testament. One presumes that he was carrying it round with him following Trenzalore, given he's on a new regeneration cycle and doesn't know when/if he might next die for the final time. Also, if he knew what the device did - and he seemed hazy on the point - then why wouldn't he have spent the entire season trying to get into it or open it.
Alternately, as it was Missy that gave Clara the device in the first place, he may have been confused about what it was - but then why carry it round? And again, if he thought it was a clue as to the location of Gallifrey, why not spend the time trying to work it out? It was obvious it was always going to be some kind of TARDIS-like Timelord tech.
Unless this all gets wrapped in in some neat little bow - that will likely involve a lot of handwavium and require significantly greater amounts of disbelief suspension - in the final episode, then i can't see how they haven't just wasted an opportunity to develop Capaldi's Doctor by showing him as a real man-on-a-mission for a season, rather than the typical bumbling-dandy that The Doctor is generally portrayed as. Like The War Doctor (as excellently played by John Hurt), but on a mission of peace.