China has been stable for many, many decades - long before living standards were rising. And it's only (short lived) protests in 1989 were also at a time of rising living standards. So I wouldn't say that it's something that comes with prosperity or conversely, that the poor aren't concerned with.
Democracies do not have more checks and balances: they have a different voting system. Unless you wish to expand the meaning of democracy (but that might be confusion).
The checks and balances are the strong civil structures like having adequate laws, a government which tends to acts within the law, and courts which can enforce the law. An example of this is pre-handover Hong Kong - no democratic process at all, but no-one too bothered about it.
I can see that Libya is topical, but the OP was about whether it is ever right to become too enmeshed in another country.
Is it really up to one group of people to enforce their view of society on another group of people, or are groups allowed to self-determine? Though that may lead to the dominant group in a unipolar world taking action (including military action) beyond its borders on the grounds of "regime change", despite that regime being legitimately constituted within the "target" country.
It is also worth noting in this context that a few friendly exiles do not necessarily transfer into a sustainable successor government. Such individuals may have the ear of the internationally dominant government, but do not appear to have the necessary backing of those who struggled in country for change.
I think the latter is an important factor in the difference between the successful "revolutions" of the former Soviet bloc (economic difficulties, but political success), all of which were home grown and none of which had outside aid during the revolutionary phase.
This even included the break up of some of the countries: Czech Republic and Slovakia being a good example. Yugoslavia - a recent "imposed" state, created by outsiders in the 1940s however, is a lesson in how it fails (only Slovenia detaching successfully). But worth noting that both Iraq and Yugoslavia were post-WW2 artificial creations - lines drawn on the map, and no real regard to the history and wishes of those whom lived there. Both remained stable under dictators, and crumbled, despite massive intervention, when the dictatorship ended (one precipitately under invasion, one more slowly but very bloodily).
Was it right for the West (ie the WW2 victors, now the P5) to impose their view on statehood on the map - pretty major interference in the role of statehood? Have many of the current troubles their roots in those postWW2 settlements?