That doesn´t hold, that island has never been a big buyer of US or anyone else weapons, the Military budget and pressure from China is a constrain. So doesn´t "worth the penny".
China is not "scare" about the "ambiguity", because there is not ambiguity, the reason why the US has diplomatic relations with China is because the US recognize that Taiwan and China are one and the PRC is the legitimate government. The US pretended that someday the KMT will take over the whole China. The moment the US establish diplomatic relations with the island, China will pack their things and expel US diplomats from the mainland because a country cannot have two governments.
Military speaking China know that they are going to fight the US from their continental size country while the US will have to rely in far off bases and boats, that was a problem in the 80s, 90s, 2000s and today. The issue that the Chinese know if they go to war for that island, they will go full force and if you had ever seen a map of everything of value on that island is a narrow band facing the Mainland. The damage is going to be disproportional in a full blown war and Taiwan province will be in ruins. They don´t want that.
So it seems that for now China is preparing mentally and military to either waiting for the US to declare formal relations with the Island and cut with China or put enough pressure to cut a Macau-HK deal with the Island.