Speaker Dimple

Used and not so sticky Scotch tape - try something not sticky at all first and gradually work at it using scotch that is newer or stickier until you can just get enough stick to pop it out.

Don't start with duct tape or something powerful as you may damage it. As far as audible - for sure this kind of thing is audible as you will get breakup modes that you normally would not see in a proper dome. It would sound like digital hash. As anyone who has pushed in a ping pong ball can attest to - once you break the spherical shape it loses strength/rigidity.

Use a guard of some type or rest your arm against the face of the speaker, hold the vacuum nozzle firmly in both hands and gently move the nozzle toward the dome. Don't get too close or you are going to have difficulty controlling the nozzle

I read about that method in Dr Comfort's "Joy of Audio" - never tried it though ;-)

Not true in my system. Imaging is spot-on.

It would indeed be more subtle than that.The dimple is a weak point that will succumb to flexure. The other issue will be dispersion. Think of how a phase plug or a waveguide changes the off axis response of a driver - same thing with a tweeter.

It is easy to show there will be a difference. For example, if your dimple is 1 cm deep right in the center of the tweeter then you will have quarter wavelength cancellation and a dip in the on axis response centered around 8500 Hz. This is probably not as bad as increased breakup or flexure though - as it may simply resonate/flex rather than behave as a piston and lose high frequency output/efficiency.

Remember that ring radiators do behave differently - so a dimpled tweeter will too.

Once you fix a soft dome then provided there is no permanent damage or crease then it should be as good as new (not unfortunately the case for a metal dome which will be toast)