Sort of useless. It was not a first class naval base by any means in 1914 and the Asiatic Squadron spent as much time with their British cousins in Hong Kong as they did at their own port. Shore establishments, repair facilities, and even vendors and contractors for coal and perishables were all key factors beyond just location and climate that make a port a good naval base.

Even then though if we assume for a moment even Japanese neutrality the port is a poor location to prosecute a naval war in Asia from. Too far from British Asian holdings to maintain close blockade it was also even farther from the Dominions of Australia or New Zealand to interfere with the flow or shipping to and from the empire. A ship which left Tsingtao to raid in the South Pacific or Indian Oceans was essentially going to have to operate as if it had no home port. Indeed that is what we see the few German raiders which Spee either dispatched or did not meet with.

Spee himself too with the largest concentration of German naval power outside Europe elected NOT to return to the port. But instead embark on one of the most remarkable and tragic cruises of the war. Taking his squadron all the way across the Pacific to South America, meeting a polyglot British force at Coronel and finally their own destruction off Port Stanley in the Falklands.

Like most thing when it came to German Imperial holdings it was the appearance of the matter more than its utility that mattered here. Britain and France had Far East naval bases and Russia had the main one taken, so Germany had to prove it could too!