As a rule, are questions about general sightseeing on-topic?
I believe that this is one of those questions which is grey in matter and may or may not be on topic? That said, I sense many of these questions should be considered off topic.
Valid sightseeing should not be an invitation to basic trivia style questions. An example of that was a recent question, which was deleted by its author, asking which covered bridges could be driven across in Maine, United States. They should also not just involve simply numbers, like (How many trees are there in California you can drive through?) These type of questions, in general, do not add any real quality to our sight and could be an open invitation to some generally watered down questions about The Great Outdoors.
As already mentioned in the comments questions about sightseeing are on topic at Travel SE which as to date has some 228 sightseeing questions and would be a more reasonable place for more trivia like questions than here.
Valid questions about sightseeing in The Great Outdoors must refrain from any sightseeing questions at a distance. In other words sightseeing while driving on any major highway (such as a Freeways, Interstate Highways, Motorways and so on) which in general should be looked at as simply high volume access routes for vehicles. It is just too open a subject for this site.
Good sightseeing questions must be limited to a particular area or region and should not include large portions of any country such as the entire state of California and must be limited in someway to the thrill of being outdoors and enjoying nature as in more remote areas and smaller states such as Maine.
My wife has mobility issues we both love the outdoors, so I can see how this question could be of interest in disability-options.
Some examples of possible good sightseeing questions:
What high (above the tree line) mountain roads are publicly accessible in Troms, Norway?
Are there any good areas near Prince George, BC, where one could get an occasion to enjoy watching mountain sheep while driving to the Yukon?
Are there any parks where one needs a permit to drive through for sightseeing purposes?
Do any general driving only sightseeing parks exist near Paris, France?
In conclusion, general sightseeing question should be on topic, but must not be too general in nature or simply too trivial, even when used as a disability option.