In all fairness, grouping how a character is treated in the Burton and Schumacher films isn't really fair. Sure, Gordon comes across as little more than comic relief in Batman & Robin... but so does Batman for the most part. Does that mean we should consider him a buffoon as well since you are grouping Burton and Schumacher together?
I don't believe Gordon comes across like this at all in '89 and Returns. Though we don't get to see much of him (more on that in a bit), I never caught a moment of him being a "bumbling idiot" in either film. In '89 especially, I think we see him more as a clean cop trying to do his best in a town filled with corruption. Him trying to get the drop on the dirty cop Eckhardt, walking into the firefight at Axis, first on the scene at the cathedral, etc etc etc... Every moment we see of Gordon in '89 portrays him as a commissioner doing his best to clean up the town while rationalizing what he thinks of this new Batman character... Hardly a bumbling idiot.
As to the Nolan films spending more time on the character... I think sometimes people forget what kind of a task Burton and the producers of '89 Batman faced back in the day. They didn't have the benefit of knowing comic films worked, or a public that was already familiar with how the comic versions of these characters were portrayed and interacted, or even that comics weren't just "kid stuff"... The public at large knew Batman as the Adam West TV show. Putting out a Batman film that totally went against the public's perception of the character, bringing it back to its essence, meant that a lot of time had to be spent on the main characters- Batman and Joker. Pretty much every scene in 1989 Batman is used to do this task. Shoehorning in more Gordon stuff would have cut away at any time the filmmakers needed to get Batman back to what he was and erase the sigma of the 60's show. Given the whole view of what that film had to accomplish, sacrificing time on secondary characters was the right move.
Nolan had the benefits of knowing comic films worked. He had the benefit of the Burton films flipping the public's opinion of Batman from the campy 60's version back to the Dark Knight (as evidenced by the crash and burn of the campy Batman & Robin). He had the benefit of comics being more in the public eye. He had the benefit of Batman The Animated Series (and successive shows) introducing and expanding the secondary characters to a mainstream audience, pushing them into almost first-string status. With all that groundwork done for him, spending more time Gordon makes more sense as his films didn't face quite the uphill battle that Burton's did in their day.
Sallah