I think a lot of it too is that not all of us "know" the original quite yet. Personally, I'm starting with the 2003 series and working backwards (ie. next is the 80's series and after that the 60's series, though I have already viewed the pilot episodes of all three). I'm doing this at the rate of one episode per week (though for 2003 and 80's, I plan to watch in both English and Japanese versions back to back in one sitting), so it's going to take a while! I also plan to read the manga and have the first 2 volumes ready to go (but am reading The Astro Boy Essays at the moment and probably will start after that). So in short, I'm much more familiar with his movie and 2003 self at this point, so it's easier to say what we'd do.
That said, I'm an only child, so...ummm...without hopefully sounding too strange, I kind of think it'd be cool to have brother (if Astro wanted to be of course).
The caretaker part of me kind of wishes I had a younger brother to look after as I've really never experienced that and seem to have a sort of caretaker personality, while the child's heart part of me (I'm actually in my late 20's) always kind of wished for an older brother who looked after me. Astro's unique in that he fulfills both - he's younger and still is full of wonder and the need to be looked after/nurtured, but he's also mature enough to be supportive when nevessary and nurturing/protective as well.
Of course I'd love to go flying with him if he'd take me! That would be amazing! And I'd love to really just have someone I could trust that much. =)
I think I'd want to introduce him to my other great love in fiction, Doctor Who, and we could watch that together.
And I've always wanted to (and hope to someday) visit Japan, so maybe we could go visit the Tezuka Museum and see where he was born, etc. [This of course assumes paradoxes are okay considering Astro's real in this scenario.] He could take the lead in Japan since he can speak Japanese and I can't (but maybe he could teach me over time). ^.^
If Astro could learn to eat and taste (I don't know if this is something ever covered, though I remember in one of the pilots he tries and empties it through his chest door discretely so as not to disappoint his father - no indication he tasted it tho') I'd cook him some Thai (I can cook some pretty mean Thai dishes including curries and soups and such; my list of recipes is limited but growing).
Finally, I think it'd be nice just to hug him, maybe watch a movie and cuddle and fall asleep or something looking after each other. (Yeah, I'm a sap. ^.^)
) and then we could go malling. Or maybe we could all go to Disney World, and Astro could laugh his head off at all the audio-animatronics. 
