I think too much of this discussion devolved into how two spells in particular work. I think the more general thrust would be, given the spells and items in the game, what would a game world realistically look like? Does a setting like Forgotten Realms really work from a magical perspective? For example, take a wall-city or castle. Neither are effective at stopping aerial or teleporting opponents. Spells like Passwall render them moot as well. Plant Growth and Fabricate are just the tip of the iceberg.
I figure the purpose of castles is against goblins, bugbears, orcs, ogres/trolls/etc, and so on. These rarely have access to spells 3rd level and above (with the potential exception of hobgoblins, but those act more like nations than wandering bands of monsters like the other goblinoid/orc/giantkin types).
So you find castles in areas near a frontier between humanity/dwarves/etc and monster-inhabited wilderness. In areas surrounded by civilization for hundreds of miles around, where the primary threat is other nations of organized humans/dwarves/elves etc, you wouldn't find castles (except historical ones left over from centuries ago when they
were useful). Instead, fortifications would likely be underground bunkers (still vulnerable to
earthquake, but I figure 8th and 9th level spells aren't really common enough to be taken into account in that way, whereas 3rd-4th level stuff like
fly and
dimension door are.)
Also for those that suggest a wizard would have something better to do with their time, you have to look at all of the options a wizard has available to them. The economic theory that governs this is called Comparative Advantage.
To a degree. But I also think that there is a factor that doesn't apply to economics in a technological world, because people who get to the levels where they can
cast 3rd+ level spells (tier 2) are highly driven personalities with their own goals: they're not necessarily going to act like "rational economic actors". (I figure there is also a bit of a cultural factor in the "spellcasting subculture", where once you have enough to be comfortable/not worry about supporting yourself, the general attitude is that making more money is a distraction from the
really important stuff, magic itself. Now there are definitely powerful mages who go off into wilderness/frontier regions and set themselves up as lords, but even that's more about power and independence than wealth per se.)
The spells listed in the game are primarily those used in adventuring, but it would be easy to imagine spells that would not be used in adventuring but would be used by the general population. For example, a lesser version of Prestidigitation that can only "chill, warm, or flavor up to 1 cubic foot of nonliving material for 1 hour" could be super easy to learn (or make a wand of) would be a bartender's/chef's dream.
Oh, I figure these sorts of things absolutely are used widely. (And the regular cantrips too - elves are pretty numerous in my setting, and all high elves get one cantrip - and I figure non-adventuring NPCs all have "mundane utility" things like message, mending, prestidigitation, etc. rather than firebolt or ray of frost.)
They are just kind of "in the background", things that improve convenience, save time, and raise the standard of living well beyond what a non-magical society with the same level of physical technology would have.
