After all there's and obvious disconnect between the various spy agencies and political process, with the former typically giving less than lip service to most treaties/laws in the past.
After the reunification many rights of the Nato allies (and especially the US) were still protected.
Germany would need discuss with the allies how to change these older treaties. Plus it would also need to discuss with the US the shutdown of various activities of the US in Germany and against German interests:
* spying on Germany on German ground. The US has lots of installations here.
* spying on Germany from the outside (like tapping communication cables outside Germany which are going to Germany)
* using Germany has a base for various wars (Iraq, Afghanistan, various conflicts in Africa). For example the US has the Central Military Command for Africa in Germany. Drone strikes are coordinated by the US from Germany. The US has logistics centrals for their intelligence agencies in Germany.
* using Germany for various extremely unpopular actions, like using Germany as a transport hub for kidnapped people who were brought to torture camps in Europe or even to places outside Europe
etc.etc.
I would be very meaningful in a symbolic sense. Germany and most of Western Europe are used to seeing themselves as close allies of the US since WW2.
With close allies you expect to be able to reach an acceptable level of trust on topics like spying, even though you know both sides are still going to do it at some level.
By not being able to sign this agreement the message for Germans / US relations is "we trust you just like we trust the Chinese". That will likely lead to a weakening of past alliances...
"Welcoming the fact that the German people, freely exercising their right of self-determination, have expressed their will to bring about the unity of Germany as a state so that they will be able to serve the peace of the world as an equal and sovereign partner in a united Europe;"
"(1) The French Republic, the Union of Soviet Socialist Republics, the United Kingdom of Great Britain and Northern Ireland and the United States of America hereby terminate their rights and responsibilities relating to Berlin and to Germany as a whole. As a result, the corresponding, related quadripartite agreements, decisions and practices are terminated and all related Four Power institutions are dissolved."
"(2) The United Germany shall have accordingly full sovereignty over its internal and external affairs."
Sorry to insert fact...
The National Security Agency was the only American intelligence agency that was aware that East Germany was to take action to deal with the brain drain problem, i.e. the outflow of East-Germans via Berlin. On 9 August 1961, the NSA intercepted an advance warning information of the East German Communist Party's plan to close the intra-Berlin borders between East- and West-Berlin completely for foot traffic. The interagency intelligence Watch Committee assessed that this intercept "might be the first step in a plan to close the border." This warning reached not U.S. President John F. Kennedy until noon on August 13, 1961, who was vacationing in his yacht off the Kennedy Compound in Hyannis Port, Massachusetts. While Kennedy was angry that he had no advance warning, he was relieved that the East Germans and the Soviets had only divided Berlin without taking any action against West Berlin's access to the West. However he denounced the Berlin Wall, whose erection worsend the relations between the United States and the Soviet Union.