Yes, I did pick a street in the downtown core as my example, because I think it’s more important for street parking to be mapped there than it is almost anywhere else, precisely because there are so many restrictions. That said, what also prompted my question is a somewhat controversial new municipal government policy that homeowners are charged an annual fee for residential parking permits, where permit zone restrictions exist. (Believe it or not our municipal government used to just hand these passes out for free!) There are many parking zones, with varying restrictions block-by-block outside of the downtown core, none of which have been mapped at all. I just thought, “Y’know, that’s probably something that would be quite useful to have mapped…”
Likewise I don’t think it’s worth tagging this info if it isn’t tagged complete with restrictions and conditions, because as you wrote: if the orientation/position is the only thing tagged, the default assumption is that parking there isn’t conditional.
That said, I disagree a bit with your own personal ‘rule’ to not add data that you’re not personally willing (or able) to maintain. Everything on the map is somewhat fleeting; at least in my little corner of the world, old buildings get demolished and replaced with new, roads are demolished and rebuilt with new, businesses close and re-open all the time. I can’t maintain it all myself, so if I followed your rule I’d just not contribute at all. But I’m being a little reductionist and absurd here 
I think what you mean in spirit here is that by its very nature these sorts of parking restrictions are easily changed by replacing a few placards on signposts. In reality these parking restrictions are actually quite longstanding; for the exemplar stretch of 5th Ave SW between 5th and 4th Street, other than the implementation of automated plate reader enforcement and the use of parking zones in place of curbside meters about 15 years ago, the underlying no-parking and no-stopping restrictions have been there for as long as I can remember (20 years or more).
Appreciate your input!