The FISC most certainly does use the Fourth Amendment as a major part of the justification of it's rulings. The "secret ruling" that the EFF and ACLU are trying to view was a FISC ruling that held that on at least one occasion the government had conducted surveillance that was unreasonable under the Fourth Amendment (http://www.slate.com/blogs/future_tense/2013/05/29/ron_wyden...).
> "The most important way the courts have shaped 4th Amendment jurisprudence in the last century is through application of the exclusionary rule in criminal cases."
I think this ignores a large body of civil case law built up around wrongful arrests and vehicular searches. Both of these are examples of active jurisprudence over the last century that directly pertain to Fourth Amendment violations.
A violation of the Fourth Amendment is not acceptable simply because they don't use what they obtained in a criminal proceeding. There are a massive number of ways that the government can harm you with the information they collect without ever filing a criminal case.
The fact that those warrants then never lead to ordinary criminal cases is precisely the point.
All federal court decisions are treated by the federal government as law. The Supreme Court just happens to have the last word on appeal.
Generally speaking in the U.S., "the law" is not what the text of a bill says, it is what the courts say the text means.
> And then there's the fact that "the FISA court hears from only one side in the case—the government—and its findings are almost never made public."
Grand jury proceedings are also secret and hear only from the government. That is ok because a grand jury is not determining guilt, it is just deciding whether a prosecution can proceed. Likewise, FISA is not determining guilt, it is just deciding whether an investigation can employ certain tactics and technologies.