As long as you have one spare place you should be able to do upgrade residential/tokyo/london/paris zones missions. Just start a new building in the empty spot, no need to have full coverage of all services. Then upgrade the building which should be easy (i.e. just one special item) then you demolish the building. Repeat. (this didn't work a couple of weeks ago if I remember correctly)Disclaimer: this works for me on lvl 29, might be different on higher levels. see my guide http://answers.ea.com/t5/SimCity-BuildIt-Strategies/Being-competetive-in-Mayors-League-without-spending-real-money/m-p/5389133#U5389133
If you have no space at all then you can demolish the cheapest service building (unhappy sims) and thereby getting enough space to start a new building. Start new building, upgrade, demolish, repeat, rebuild service building (sims are happy again). Expensive, but makes the mission doable. Disclaimer: I have never had a full city so I haven't tested this. But it should work. If you try it please let me know.
/Brian
I take your point, and indeed I have done that in the past.
