Though this hasn't always been the case for me, I currently have an oktoberfest lagering that has changed a pretty good deal since i turned the temps down. After primary, i tasted it and i didn't taste any diacetyl, but the beer tasted more like pyramid brewery's amber lager (sorry if that beer is only in my neck of the woods, that's the only beer i know that it tasted reminiscent of). It had a nice, gentle malt flavor to it, and I could actually taste the lager yeasts themselves, but it didn't taste very german. I was bummed because i'm a massive stickler for german styles, but the beer was good anyway so I put it down to lagering temps.
3 weeks later and it smells like I just cracked a paulaner oktoberfest, all sorts of melanoidenny goodness going up my nose. My theory is that that 'lager yeast flavor' i tasted about was actually a more potent flavor than the german-malty-melanoiden flavor I was looking for, and as the yeast settle and eat up more of their by products, that distinct continental character was allowed to poke through. This isn't based on fact or science, just my perceptions of dozens of failed and successfull lager attempts.
Reading suggests that not lagering can result in a 'green apple' flavor from acetaldehyde which is a naturally occuring ester that usually gets eaten up. This is a known part of Budweiser's profile, if you taste it carefully enough. In my experience, green apple is one of MANY flavors I wish would vanish with lagering time =D.
So I guess lagering seems to only fix minor off-flavors. If you used just a vial of white labs and fermented at 57 degrees, lagering won't fix your problems. So brewhan, bottle it now only if you're satisfied with the flavor you have today because it will taste more like malt/hops and less like yeast as time goes on. Just check the hydrometer so you don't get bottle bombs.
I don't know anything about keg lagering though.