I agree that China has some serious structural weaknesses, and I think that they have had their big run.
Some of their bad practices are catching up to them, and the main things that propelled them seem to be running out, or in danger of reversing (e.g. they are not the low cost labor providers any more, and new money is going elsewhere to set up new business).
One big difference between them and the Soviet Union, is that the Soviets (like the Russians today) were hugely dependent on oil for the lion’s share of their economy and income. Many have pointed to the collapse in oil prices as the shot that finally killed the ailing Soviet Union.
Although China is extraordinarily dependent on export of manufactured goods (and import of raw materials and oil) as you point out, they are also exceptionally dependent on infrastructure investment. To keep high economic growth numbers, the government there has pumped out stimulus after stimulus for “shovel ready” jobs.
They have been building roads, bridges and tunnels like never before in the world. Whole cities have been built, that no one seems interested in occupying. These “ghost cities”, and their “zombie factories”, also propped up with gov’t stimulus past the point where their business case had died, has produced a mountain of debt, secured by assets that are often decaying away without producing a return. That debt will have be written off at some point.
In addition to malinvestment in projects that will never pay themselves off, these programs were rife with corruption and outright theft, which funded a diaspora of low-level Party functionaries fleeing the country with their families and new fortunes. The California real estate market is booming, driven by Chinese paying cash.
The Federal Gov’t in China just put restrictions on local governments to prevent them from issueing new debt for most types of this “stimulus” (i.e., no new project starts). Just these restrictions on local governments, are estimated to take 4% off of GDP, starting to hit this month.
It is interesting to see the timeframes that you pointed out, for the life of the Soviet Union, and that of Communist China. Even though many factors seem different, maybe there are some underlying commonalities, like the rate of corrosion - how long does absolute power take to corrupt a system absolutely? Maybe it is human lifespan - how long until the skills and spirit to really get things done dies out of the workforce?
China does have major pollution problems, but I think they are starting to feel the need to improve the situation. When I glanced over the BOAO Forum Agenda (see link at comment #133) I thought I noticed a number of sessions dealing with environmentally related issues. I also think China will be more likely than Russia to pull out of the messes they are in. Unlike Russia, they do have a 2,000 year plus history of civilization and government. Also, unlike Russia which currently has Putin, who is almost a throwback to the one man tyranny of much of Communist history, China has more of a committee based governing system. Yes, I know the old jokes about committees, but that is certainly an improvement over Russian style one man rule. Even though the Politburo has been a committee of sorts, I don’t think it has/had the power and flexibility of the Chinese version. I get the impression there is a somewhat successful crackdown on corruption especially in smaller cities and villages.