"1) China has huge corruption yes but it shows no signs of bursting into anarchy, democracy would be a good thing for the people though."
Its on the brink just like Iran or libia. Libia already bursted. Democracy does not grow in 2 years. Its a slow proces. It would be good, but it would also mean a slowed down growth in the short run and there is always a period of anarchy during periods of transition, doesn't matter what the name.
Let me note however IF it became democratic, how it will be much easier to make agreements between the large power blocks as it will be regarded as less dangerous. Its very hard to predict the future then.
"2) China is increasingly wealthy cost increases will be affordable as their economy grows."
their wealth isn't growing as fast as it did. And it will only slow down. With the average chinese being very poor and ever increasing costs, it will only worsen. But their neighbors grow wealthier as well, and Russia is a rising star with resources and farmland abundant.
"3) the population of US and Europe is ageing too."
Its not even comparable.
"what China will get in future is increased immigration and decreased emigration as their economy grows which will go some way to reduce the ageing."
where will they come from then? China probably holds 2 bilion people unoficially.
"4) food prices will affect america and europe too."
But less, as the average person is rich, and also because they have a much larger food production.
"a) the Irish economy has a different profile and isn't comparable"
fair enough...but all econs growing from nothing show the same profile. How about them?
"b) foreign investment may lower but china has now got some huge domestic corporations."
...in trouble as export will also lower and resource prices will rise.
"c) china like all countries will have to deal with ageing while europe and US has had a favourable situation with regards to little emigration and high immigration as China becomes wealthy they will be more attractive to live in."
Europeans treat foreigners kind compared to China. But its unlikely to become "open" that way. They cannot afford the security risk.
"pollution is unlikely to cause massive instability in china. unless it's nuclear radiation."
In some areas 1 out of 3 children have 6 fingers. But those spectacular events are only small compared to the air pollution comparable to ours in the primal industrial area.
"corruption allows china in some ways to pass projects that democracy would prevent or massively slow down in europe and us."
You're talking about decision taking, not corruption.
"China is investing heavily in sourcing food from affrica. food prices will go up but that will be a problem for everyone not just china."
but the lands with food production will gain more from it, while china has none, and its inhabitants no money.
"china is working to bring inflation down. it's lower today than it was in 1994 for example."
Only due to a global crisis. But its easy to step down from 1994 and still have waaay to much inflation.
"China is increasing military spending by about 12.5% p.a. (though it has varied over the last few years) but despite the loud warnings by the US and her allies China spends less than a $100 billion on the military. compared to America which spends closer to $500 billion."
But a lot more then before. They can't use it if they don't increase it. Nobody can predict the future but chances are they will make the same capital mistake the soviets did.
"Europe may be culturally more similar to America but as I've said before the EU nations can't even form a single EU state, moreover the alliance with the US has meant Europe has long neglected spending on defence."
giving more resources to their economy. It doesn't need to be one state to mean something. If north africa will become democratic as well, china will be even more isolated. On this moment aproximately only 40% of world's countries is authoritarian and by no accident less rich, powerfull and infuential.