Well, of course, it's just opinion because the only way to know would be to allow the yuan to float freely which it does not. So ask yourself...what is the most important objectives of the Chinese government?
It's pretty clear that near full employment and export markets (37% of GDP) are what the Chinese need to continue to fuel their GDP growth and maintain stability politically. Their domestic market is in its infancy so the best way to do this is peg their currency for strong exports. They can't switch from external to internal demand as a economic driver.
If they allowed their currency to float freely I'm not sure you could find anyone who believes it wouldn't trade very strong but hurt their main goal, employment.
Here's a piece that can give you a baseline on valuation.
http://www.voxeu.org/index.php?q=node/3666
What's interesting is eight of the eleven Asian countries within the top thirty economies (the exceptions are India, Indonesia, and Korea) are on the list of significantly undervalued currencies, and the list is dominated by eight Asians out of eleven countries on the list. This simply suggests the not so controversial view that Asian countries have undervalued their currencies as a strategy to generate employment growth with China leading the way at 40% overvaluation.
I think a more provocative question is China's exports currently account for about 10% of the world's exports and are almost tied with Germany for the No. 1 position in the world. If these numbers continue to grow at their historic 25% rate (and world exports at their historic 10% rate), then by 2020 exports from China would account for almost 50% of the entire world's exports. Is such a situation is economically and politically possible? I would suggest not for two reasons but no need to clutter the thread further.