Hello again! I was just watching Arthur yesterday since they were showing new episodes this month. (Needless to say, I watch a lot of "edutainment cartoons" due to lack of cable)
Surprisingly I found that in yesterday's episode (Agent of Change) had a sort of Astro parody making a brief appearance on a poster with a bunch of other spoofs of children movies released within the last few years. He was called "Donny Droid" or something like that. Unfortunately due to bad timing I don't have any pics but I did see it! If the episode pops up again, I'll try to get pics!
I know this isn't an Astro cameo, but in the Astro Boy movie comic when Toby is in his classroom, Pinoko (and I think a young Rock) are there as students. Pinoko makes her classic face too lol.
I can also see Tezuka's mushroom pig in the far back, and the teacher seems to resemble Mr. Mustachio.
You know, it's kinda nice. Most American movies completely ignore or are uneducated about the source of a series, but they actually paid attention to Tezuka's Star System with this. Even Tezuka himself makes two cameo appearances in the film.