Sorta late to this, sorry, but maybe I can still add something of value.
First, a bit of history for the Quetico part of the database, for those who aren't familiar with what happened before Paddle Planner took it over. The Quetico campsite database was originally built by Arch Harris and called "Paddler's Campsite Database (PCD)". (Was this 15 years ago? Something like that.) Arch collected campsite locations from various public sources and showed them on a single map, which users could interact with, post comments, add new site locations, etc. The public source data were of varying quality (some sites were located incorrectly, some did not exist at all), so the first big step (collecting all the public data) could be improved even more by user input. A couple of years ago, Arch retired and was looking for a new home for PCD. Ben Strege stepped up to the plate, and incorporated PCD's data into the predecessor to PaddlePlanner, with a slick new software interface, plus all the other PP features (Thanks again Ben for saving this huge batch of valuable data from oblivion!)
PCD's original software was state of the art at the time, but it did have some limitations which don't exist today. The original PCD rating scale was 0 to 5 stars, with a "0" signifying "Not a campsite", so that's where that idea came from. When things were converted over, Ben chose to define "Not a campsite" separately from the star ratings, so if a site did not exist, it did not get a rating, and if it did exist, it was rated from 1 to 5 stars.
This was a definite improvement, since in most cases, a zero PCD rating did not mean a location that was one step worse than a 1-star, but instead, it meant that the paddler could not find a location at the spot indicated on the PCD map. I have found more than a couple of cases where a previous user marked a location "Not a site", but in fact there was site at that location. Sometimes the 0-star rating meant the previous visitor found the site but it was so poor that for him it did not rate even one star, often it meant the site was small and/or hard to see from the water, and sometimes it meant the previous visitor was either blind or in the wrong location and zero-rated a large and obvious site. If one paddler cannot find a site and gives it 0 stars, while a second paddler finds the site and rates it 3 stars, is the average 1.5 stars? Or 3 stars? If PP decides to allow a zero-star rating to indicate an unusable site, it would have to ensure that the user actually found the site in question and hated it, not that the user was mistakenly staring at some random patch of forest and not at the actual site.
Should there be a formal scale for ratings? I think yes, but only in the most general sense, for example "3 stars" means "average-comfortable", or "1 star" means "usable if desparate" or something like that. We all have different criteria for what we like in campsites, and so our campsite ratings should be expected to differ as well. Trying to pick one formal set of criteria for "campsite quality" and having us all rate sites based on that will mean that the results will only be of value to those of us whose personal criteria match the formal guidelines. I'm happy using the average star rating to get a rough idea of which sites are decent, and then reading through the comments to get a better feel for how well it fits my own personal likes and dislikes.
Half-points? Yes, for me there are a lot of cases where a site falls between the 1-star, 2-star, and 3-star categories and I'd find the extra precision useful. Usually I will include the half-star ratings in my comments, so people will know that a site to which I gave 3 stars (2 1/2 stars) might be a 2-star site to them, and a site to which I gave 3 stars (3 1/2 stars) might be a 4-star site for them. If two people rate a site, and one gives it 2 stars and the other 3 stars, the average is 2.5 stars, so allowing half-star ratings from single users really doesn't change anything. The important thing is that any changes we make to the current system don't make the thousands of existing campsite ratings already in the system obsolete.
To sum up this long winded post, I think the current system is pretty good. The biggest improvement that could be made would be for more users to submit more campsite ratings, with more detailed comments, more photos, ...