Personally, I don't believe it caused any more wear and tear on equipment than what a 10 pps dial would make on the system. Since panel, #1XB and #5XB all used common control and didn't do anything til the requisite amount of digits had been entered in the receiving registers likely could care less how fast the pulses came into the registers. And I don't think it caused any more wear and tear than receiving MF or DTMF.
Wear issues weren't likely the problem with 20 pps dials o n SXS. The problem is that SXS systems cannot keep up with pulses as fast as 20 pps. It might work *sometimes* but for constant reliable service 20 pps dials would not likely have enough reliability to be used.
As for "why subscribers were never given 20 pps dial phones as a usual thing" my guess is that WECO never put that into widespread production so it wasn't made available as a standard dial in a standard 302 or500 (whichever would have been in use at the time.) When Touch-Tone (DTMF) came out in '64 it was a viable option that was going to eventually be implemented throughout the Bell System eventually. Whether this is the reason or not is only my speculation.