I got a walk up at CRT in June, so it is possible, but I think how you approach it makes a big difference. I was in line behind a Mom with three girls all dressed in princess costumes. The Mom was yelling at the girls, very stressed out, etc (which I understand completely), but she kind of let that carry over to her interaction with the CM. She bordered on demanding a seating and blamed the CM for not having an opening. The CM turned her down and I started to walk away too. The CM asked what I needed and I explained I was there to see about a walk-up reservation, said I understood it was nearly impossible, but I figured I'd try because we (ok, really just me) really wanted to eat at CRT. The woman asked if I could come back in half an hour, I said yes, she took our name and we got seated. I realize Disney is stressful and when you have kids pulling on you, it can get hard to be nice (trust me, I've been there), but that woman lost out because she couldn't be polite. We had the same size group, so it was all up to the CM.