I am not sure whether nationalism is really unchecked. I'd say
its only as "unchecked" as the Central Government wants / allows it
to be. And fortunately, the populist has no control over the
military.
I do not believe that the Chinese wish to seek immediate
reunification with Taiwan, but rather the status quo to
remain. It will of course, constantly remind the world that
Taiwan is rightfully a part of China, but is willing to be patient
with it.
There has been friction with North Korea, especially with
regards over the Nuclear issues. I sincerely doubt the
Chinese want the peninsular to plunge into war again since it had
paid a heavy price in securing it. They are probably more
interested in reining in Great Kim's ambitions in order to maintain
the status quo.
The Spratly's have toned down over the years though IMO it
remains a potential flashpoint with over-zealous claimants.
However, most of the contesting countries hardly have the military
capability to stand up to a PLAN SAG in the near future. Again, the
status quo benefits China currently, and they have no reason to
change that. OTOH, with some of these claimants acquiring
advanced submarines, they will do well to exercise restraint in
their deployments to the Spratly's and not antagonise the Chinese
with their new "capabilities".
In a way, it seems to me that the Chinese believe that "if it
ain't broken, don't fix it." If the status quo is still
beneficial to them, or does not pose a threat to its national
interests, it probably will not pursue any potentially volatile
courses of action to change it.
Of course, these are just my opinions.