There is current no value in taking Kinmen or any of the outlying islands close to China.
There is no diplomatic, military or strategic value, and certainly no PR or propaganda value.
The people on those outlying islands will either be indifferent to or even support being taken by China. The rest of the people on Taiwan will use it as a way of galvanizing themselves against China even further.
It will also enable the government on Taiwan to more easily "give up" their claim on those islands and thus in turn reinforce their political position of being "Taiwan" rather than the "Republic of China".
Kinmen and other outlying islands may have little strategic or economic value but they are great starting points for potential PRC salami slicing.
PRC can first start with overflights of some of the smaller ROC controlled islands near the mainland, which has already been done in the recent flare up. Once that become a regular and accepted practice, PRC can start with overflights of the bigger Kinmen and Matsu islands. After that also become regular and accepted practice, we move on to overflights of Penghu, followed by islands just off the coast of Taiwan like Little Liuqiu, Green island, etc. Similar salami slicing can also be performed with PRC ships entering territorial waters of these islands, followed by boarding and inspection of ships under the guise of law enforcement.
Each incremental step in this salami slicing can also be timed as responses to provocative moves by Taiwan independence forces, such as visits by foreign politicians or officials, attempts to join international bodies, etc., to further reduce the likelihood of international criticism and sanctions.
If anything I would say that taking those outlying islands is an actively bad idea from China's pov, and that actually keeping them in play as under the control of the govt on Taiwan is more useful for China.
Yes, I agree there is no point in taking and occupying these islands. Keeping them under ROC control is far more useful from diplomatic and psychological perspective as they can be used to demonstrate PRC sovereignty over territories controlled by the ROC and make the Taiwanese psychologically accept the total dominance of the PLA.