Contrary to popular belief, I'm not a Batman fanboy; I like a selection of very good Batman stories. Good Batman stories tend to be very good stories in general (Good Green Lantern stories, on the other hand, tend to induce slightly less vomiting than other GL stories.). I love the potential in seeing what happens when Batman gets too old to be Batman. His whole deal is that he is just a man and like all men must face decay and death. To paraphrase The Bible, how Bruce Wayne faces life at an old age is at least as important as how he faces death.
Batman Beyond does that. Because Bruce Wayne is older, you've got Terry McGinnis being Batman while Bruce Wayne deals with his limitations while still getting the better parts of the 14-year blow job the DCAU was giving him. Unlike its comic counterparts, Batman Beyond really stuck to the premise of letting Terry be Batman, for better or for worse.
Compare him to Damian, who was literally doomed from the moment he was created. Grant Morrison abandoned his original plans and spared Damian only because he was such a fantastic character. Sure, it meant that Damian died a bit later, but you knew it was going to happen. Bruce Wayne had to be Batman because superhero comics are frightened, unimaginative fields where--ah, that's not fair. When it comes to certain things, DC and Marvel only have so much courage. Permanently getting rid of a flagship character so a less-perfect successor can pick up the mantle in the belief that better stories can come out of it is something that takes loads of courage.
So, yeah, Marvel has enough courage to do it when another studio owns the film rights.
Aaaaaaaaanyway, Terry was Batman in BB. End of story. They even did a good job of giving him a new rogues gallery while still using Bruce's old one. There wasn't a "What if Bruce Wayne got a robot suit?" or "What if Bruce Wayne got younger in a Lazarus Pit," except for that episode where Bruce Wayne got de-aged (sort of) by a Lazarus Pit (sort of) and, well...
...it was awesome!
 The story where he gets too old to be Batman, but continues being Batman anyway is a good story, but it doesn't count.
 There are plenty of stories where Batman dies young and virile as Batman. Great stories too. Maybe one day
 Spider-Batman, really.
 There's nothing wrong with being Spider-Batman. Spider-Man is a great character with great stories in his own right and you'd have to be a fool not to try mashing those two guys up every now and again.
 Again, nothing wrong with that. Batman got a lot of love from 1992 to 2006 and it was awesome.