We've all probably wrestled with this question at one time or another. I think of each audio component as having a performance envelope. A better amp's envelop will be wide enough to handle more difficult speaker loads etc. (better current output maybe or able to be driven harder before distortion becomes noticeable)
Where two different amps envelopes overlap they will sound exactly the same. Where they don't is where you'll be able to hear differences.
If both the amp and the speaker's respective envelopes are wide (or are compatible) you have a better chance of "synergy" between the two.
More money spent should get you a wider envelope but at some point you go beyond the performance envelope of the listener's ears/brain and you won't be able to detect the difference.
Where two different amps envelopes overlap they will sound exactly the same. Where they don't is where you'll be able to hear differences.
If both the amp and the speaker's respective envelopes are wide (or are compatible) you have a better chance of "synergy" between the two.
More money spent should get you a wider envelope but at some point you go beyond the performance envelope of the listener's ears/brain and you won't be able to detect the difference.