Whenever I fly PA28s I prefer to fly from the Right hand seat. Aside from the benefits of being able to make sure all passengers are seated and belted in before I clamber in myself, the simple, selfish reason of being closest to the emergency exit is the deciding factor. The fuel selector isnt ever a problem - if i'm by myself, I just lean over and switch it. If I have passengers, its often possible to get them to move it for me (with, of course, appropriate monitoring and confirmation by myself also) otherwise I just reach past their legs.
Parallax error on the ASI is most pronounced at around 100 knots - and if you're flying Base or Final at 100 knots in a Cherokee then perhaps the choice of seat you're in isn't the biggest problem you have that day. Get the speeds down below 80 and parallax virtually disappears.
Each time I reset the DG, I just make it look right for me, which actually means I compensate for the error, and the person in the LHS actually sees a skewed DG. No dramas, it works for me.
However, after happily flying them from the RHS for many a moon (the operating handbook does not prohibit this in the PA28), I embarked on a survey of instructors around the country. This was, of course, an informal survey, but each and every instructor from expensive city-based schools informed me that it was either flat-out forbidden unless you have an instructors rating, or that one needed a specific RHS endorsement for the particular aircraft
Sorry, boys, there's no such thing!
Also without exception, the rural instructors who actually teach flying more so than obedience all told me that it was perfectly acceptable unless specifically restricted by the POH. This is the viewpoint that makes sense, and agrees with my own research.
The cynical side of me is amused that the schools who charged outrageously expensive rates were happy for me to undertake a few hours dual with them to be 'signed off' to fly RHS...