I don't think Bruce had actually been a recluse for the entirety of that 8 years. 5 years into that timeframe, he was pouring money and resources into the fusion reactor project. Surely that would've required him to maintain at least some sort of public presence, at the very least at Wayne Enterprises if nowhere else. After a second viewing, my impression became that he was only a recluse during the last 3 years prior to TDKR, and that the need to shutter the reactor project compounded his grief over Rachel, driving him into seclusion.
I don't remember her exact dialogue now, but during the very first conversation between Bruce and Talia-as-Miranda, she made an observation about the reactor project and his seclusion that implied he didn't vanish until after the project had been shut down.
The issue for me is that Bruce Wayne is a driven personality, he requires strength, conviction, AND obsession. He doesn't just stop being what he is (Batman, among other things.) The depiction in the Nolan films shows someone who used the Batman persona temporarily to make a point and then fucked off. Kind of like an internet message board identity. It's not who he is. For Bruce Wayne to be Bruce Wayne/Batman, he should be thoroughly committed.
I appreciate in the Nolan universe that Bruce Wayne essentially fell apart when he stopped being Batman. His psyche is intimately tied to Batman, and to Gotham. If Gotham ceases to be, or changes radically, so too does Bruce Wayne cease to be. This is a pretty clear portrait in the story and kudos all around. That said, Bruce Wayne exists because he has extreme personality disorders, just like the Joker, et al. He doesn't just happen to stop needing to have the Batman persona to be able to deal with his personality needs.
In saying this, I like the story, and I don't. It touches the reality of the obsession and need, then it backs away from it. I don't feel it totally works as a character study.
I don't like to compare this film to Avengers; Avengers was like a symphony - it isn't about logic, it is about a trip from start to finish that leaves us thrilled. Nothing wrong with that and it does what it sought to do. TDKR is a different intent and different process. Does it do what it intended? For me there is some mixup in there.