I'd say duplicating things in an eVar AND a prop used to be a common (even a best) practice but agree with Gigazelle​ that it isn't needed as much anymore, because Adobe is continually removing barriers that used to exist between "traffic" and "conversion" information. Because they aren't needed to ...

Add my votes to:crossVisitParticipationtimeParting (note- the DST values need to be updated, we're going in to 2019)getPercentPageViewed (not my favorite, but lots of folks still want it)appendListhitGovernorgetPreviousValue (see my note above as to why I still see this as needed)getValOnce (I'm sur...

Beautiful list!I do disagree on one point, though:  I'd say getPreviousValue is NOT replaced by data element persistence, unless you're VERY careful about timing- if I want to set the previousPageName, my PageName data element is going to return the CURRENT pageName, regardless of how long I told it...