Recheck the tweeters again and visually look for any creases that may be left on the dome or at the surround circumference. My recommended method for pulling out T27 domes is to gently "suck" them out personally - works better than a vacuum method (better control).
If there is a crease at the circumference, the voice coil will be non-circular and probably rubbing/hung up on the pole piece. Anything more that a few small dimples/depressions left on the dome will affect its shape and the voice coil but its very hard to get all the dimples out once the cone had been inverted.
If you test both drivers out of the speakers, put them on an amp that has some type of tone controls - turn down or off any bass and midrange control and turn up about 1/2 way the treble controls. Then try playing some music with known high frequency content (Brasil 66, Greatest Hits, lots of sibilance). Don't turn up the volume too high because tweeters don't handle a lot of power. If it still seems like the tweeters aren't playing loud enough, then they have probably been damaged in the past.
If they play plenty loud, then try the same test with them wire in the speakers (or do this first before removing them). Then the problem will likely be in the crossover. Look for any resistors that may look burned, that is a giveaway that the speakers were overdriven in the past with high-freqency content or an amp went ballistic on it. I agree with replacing caps as the crossovers are well over 30 years old now. If you do replace caps, the recommendations above are fine and you should replace one channel first and see what the differences are compared to the stock other channel.
Regards,
Bart