interesting idea. never thought that way, consider myself a real ICS-sucker
does this really work on the higher levels? AI civs can be really nasty towards smaller civs...
on terms of realistic or not, a given factor must be that the city has all the resources available to build a space shuttle and such improvements.
and after what we´ve seen so far, civ III will contain alot more unique resources, making trading a of bigger importance to keep your cities top trim.
this will make the player having to build a few cities himself, to buy everything would probably be to expensive if the city´s priority is science.
SO, i don´t think we have to worry....