Hmmm... Just add a spell to conjure monsters and you've got the Gauntlet video game translated to D&D...
Heh. Potentially, yes. Any spell you like can go in there, as far as what little rules there are for magic device traps are concerned. Summon Monster Y, Summon Nature's Ally Z, Summon Elemental Swarm, whatever.
However, when speaking along the lines of beneficial spells, the general thing to do is make a soup (or other bland food of your choice... which isn't bland when served, thanks to a cantrip) kitchen:
"Traps" along the waiting line for getting the soup:
Cure Light Wounds
Extended Endure Elements
Neutralize Poison
Lesser Restoration (once for each ability score)
Remove Disease
Remove Curse
Remove Blindness/Deafness
Remove Paralysis
Prestidigitation (cleaning)
The soup kitchen itself is powered by a "trap" of Create Food and Water, combined with a "trap" of Prestidigitation to make it tasty (and possibly a 'trap' of minor creation to put it all in a bag, with wooden utensils, to get people through quickly, although this is optional and doesn't really matter)
Whoever goes through gets food for 15 at the end of the line, is feeling pretty good, and is quite healthy.
Charge five coppers for a trip through the line. The untrained hireling who makes 1 sp/day can now support a family, if he's got somewhere to shelter them. If he just has himself, he needs to worry about hail, lightning, and particularly extreme weather, but otherwise can do whatever and save half his wages for retirement.
However: There's a relatively fixed number of coins in an economy! You're going to slowly choke the life out of a city doing this if you don't put all the coins back in. So hire people who are out of work - ANYONE who is out of work - initially at 7 coppers/day - to do something you want done. Yes, it's below normal wages for untrained hirelings. That's intentional - it means they won't be working for you if there's better work elsewhere... and you can demonstrate that the company store will get them, personally, well taken care of, with a little spending cash left over, and probably let them support a family, too, if they've already got suitable lodgings. You're a coin sink, and the lack of coins will slowly drive other people out of business (very slowly; doesn't matter how much your goods are worth if nobody has the coin to buy them), at which point... everyone's working for you. Doing... whatever. Making trade goods, maybe. Possibly walking the city wall with a sling and a bunch of rocks (Simple weapon, within range of a commoner-1 to know, and doesn't cost anything). Possibly dancing. Whatever. But unless something interferes (and it will - there's going to be some people who'll figure out what effect your business will have, or a local thieves guild who may disable your traps, or whatever), you end up ruling by way of having essentially everyone on your payroll.