I loved the ending and cant see what the confusion is. The expression on Alfreds face should tell you that he was alive, well and living his life at last. They didnt even need the shot of Bruce/Selina but was a nice touch and sealed the chapter. Fantastic ending.
Showing Bruce and Selina was completely necessary:
*drum roll, another TL;DR post*
Being too vague would allow the audience to entertain the idea he's died for the very cause that challenged him in the beginning of the journey - precisely the opposite of Nolan's intentions, so he didn't.
Seeing him at the cafe is important:
1) The screenplay and novel are careful to describe the deep peace Alfred sees on his face, which we need to see on Bale's face (I'm not sure how successfully Bale pulled this off). We have to know Bruce is able to be himself and not be hiding behind disguises (including his 'Wayne' mask).
2) The visual symbols that he's moved on from Rachel's death - which Tate/Talia exploited successfully - and his parents death. If we can't see what Alfred sees, we wouldn't know that Selina's there. Her being there gives the audience the following information: Alfred wouldn't have imagined her as he wasn't around to see their relationship develop, unlike some random chick the audience has invested no emotion in (as we see when he's telling Bruce about it). Seeing her wearing the pearls demonstrates he no longer needs to hide memories of parents away + the significance of giving something that important to another person as a gift.
Plus we'd have needed a separate Selina scene. This would have made no sense since her character is written into the film specifically for the benefit of Bruce's character arc and in terms of Batman lore she is "the one" for Bruce - they've been married, had kids etc.
1)
see here.
2) As well as being the catalyst for change that gets Bruce moving again (Bale described her as the person that brings Bruce back to life), she's used to embody the faith he has in people to choose to do good, and she proves his hope in people is justified. In terms of her arc, Wayne is the catalyst for her change - she'd always been looking to run away from her mistakes and it's serving Batman up to Bane only to find out he's Wayne (shattering her preconceptions about him) and then being caught by Blake and forced to live with the consequences (the siege) that we see her question her own judgement and look out for others not because she has to, but because she now chooses to (the apple, "this was someone's home" and it's edited out of the film but in the script of that same scene it's asked "isn't this what you wanted?" to which she replies "it's what I thought I wanted").
3) Bruce being the only character to see through both her acting and the barriers she puts up
4) Bruce needed a strong female character to evolve with after Rachel's death, to prove that he could move on from his time as Batman. Rachel rejected him because she couldn't deal with him being Batman, Selina embraced him because of it.
5) Her outright goal was exactly what Alfred wanted for him all along. The chemistry between Bale and Hathaway effectively showed how when they came together, they connected and let each other in.
So we need to see they get a happy ending together, and it works best when used as the reveal for Alfred because he's the one with the most emotional investment in Bruce.
