Should "quality" be affected by your film preferences, or is it meant to be an objective (and testable) hypothesis about what some group of people (critics, film bloggers, etc.) would report? If the latter, then I think the quality/rewatchability metric potentially misses information about "first viewing enjoyability," which is what I personally think is much more important than rewatchability.
In the end, I still have trouble with the "quality" metric. If it's meant to be objective, why use user input rather than some aggregation of real data (e.g. Metacritic or Rottentomatoes)? If "quality" is meant to be subjective, then it doesn't seem much different than "first viewing enjoyability," since "enjoyability" and "personal opinion of quality" seem by definition equivalent.
For example, 5 stars for quality and 0 for rewatachability doesn't tell me I should watch the film if I haven't already. But maybe 2 stars for rewatability/subjective enjoyment is enough justification to watch it to appreciate the quality?
e.g. I'd consider The Shawshank Redemption to be a high quality movie, but I have no particular desire to watch it again (even though I enjoyed it). On the other hand I can't watch enough of Big Trouble in Little China even if it's a cheesy movie.
Some of my favorites though have both qualities, e.g. Blade Runner.
'Quality' is intended to be a more objective score of the craft of the film. Quality of writing, directing, acting; originality of the idea; how influential it is.
'Rewatchability' is where your enjoyment gets factored in. We think it's important to consider 'watching it again' rather than enjoyment first time because it separates out films better. For example, the film Avatar is quite enjoyable the first time round, but IMO not particularly worth rewatching.
Btw, I'm the author of both posts :)