I think it all depends on your children. I'm 25, my girlfriend is 23, and both of us still try and get as many autographs as we can. We like to do character buffets for the popular characters (Chef Mickey, O'hana, etc.) and then spend some time waiting for "rarer" characters, or characters you can't meet during a character breakfast/dinner (Peter Pan & Wendy, Tinkerbell, Gaston, etc.)
Plus, autographs are totally optional. Either way, you have to meet the character to get their autograph.
For us, autographs are just another Disney thing to collect. In May of 2014, we saw Pinocchio in Town Square first thing in the morning. We had read that he was a pretty rare character to see signing autographs for guest, so we had to get his signature. Almost missed our O'hana breakfast reservation but it was totally worth it.