The party's position is (fairly) secure - they're certainly not in immediate danger of losing political control of the country. Attacking Taiwan would result in some pretty dire consequences, not the least of which is trade sanctions from just about every single one of China's largest trade partners.

As an export and industry-oriented economy, they simply can't survive that.

If the party is looking for a quick PR win and publicly flex is muscle, it would do much better to attack a domestic target - the international community has more than proven that when it comes to ethnic issues in China they will do little more than issue mild rebukes.