This is, of course, a matter of opinion. My opinion is that law enforcement should be able to ignore the Bill of Rights in such cases. However, this opinion is qualified by one major caveat. I believe that law enforcement should only be able to do this if it can convince an impartial judge that it has really uncovered a true terrorist plot that poses a real danger to Americans if it is not stopped.
Terrorism is, I would argue, different from regular criminality and must be treated differently. It may be acceptable to follow all sorts of procedural rules when dealing with ordinary crimes. However, ordinary crimes do not kill hundreds or thousands of people all at once and do not put the country into a panic. This justifies the taking of steps against terrorism that would not be allowed with regard to regular crimes.
However, law enforcement must not be allowed to determine when they are or are not involved in a terrorist investigation. There would be too much temptation for them to label ordinary crime as related to terrorism. This would allow them to intrude on our rights much more aggressively. Therefore, I would argue, law enforcement should have more leeway in fighting terrorism, but only if impartial judges agree that a given case is truly about terrorism.