Shit. Just wrote a longish reply, then the server wasn't responding and 'go back' in the browser doesn't restore the typed text
Nevertheless, I'll try again.
PAE is (AFAIK) derived from the DEC drift only. If - as Paul suggests - the guided info is used, there is no influence of PE on this, as it's corrected out. One has however to sum the single DEC corrections and delta t, and ignore the dithers properly. I had a quick try on that using some guide log from a few days ago:
The drifts are quite small here, as my mount sits on a permanent pier and is quite well polar aligned. And I have no idea what causes the reversal of drift direction, TBH.... (*) But from that data/graph one can extract the DEC drift in "/min and with the proper formula (that I don't have at hand ATM) compute the PAE.
Is having that available live in the guide tab helpful? Maybe. PHD2 doesn't have it, and usually one would rather use the separate polar drift align and actually
do the PA. However, it might be interesting for people that set up their equipment temporarily and on softer ground. There, PAE could build up during the night, like from the tripod sinking in, or from walking around close to the telescope...
(*) Edit: Just thought about that: It probably is the discrimination between AZ and ALT error: The early part is 'close to horizon' and thus measures ALT error, whereas the later part is close to meridian - end of guiding was actually due to meridian flip - where drift align is sensitive to AZ error....