I'm wondering, if a fair number of people have consistent access to 9th level magic, what sort of implications would that have for how "adventurer society" acts?
I'd start with thinking about cantrips and low level spells on the base society. Given that 5.5e makes staves with cantrips very cheap, these will be owned by communities, whether that is the form of nobility, council of elders or elected officials. The wealthy will have their own golf bag of cantrip staves.
Mold Earth is as effective as a 200hp excavator, able to move 6 tons of dirt, doing the work of a hundred laborers. Shape Water is like a powerful water pump, able to lift 10,000 gallons of water 15ft in a minute. Control Flames is a modern fire extinguisher. Create Bonfire can heat an oven or forge with no fuel. Mending can repair all kinds of things, like tools and furniture up to and including wagon wheels and ships, assuming the boards are each less than 12" wide. Guidance can assist artisans, scholars, and performers.
Low level ritual spells can be cast without concern of spell slots. Unseen Servant can let one caster do the work of six grandmothers/children. Weeding, picking fruits & vegetables, collecting destructive insects, picking stones from fields, etc. A Floating Disk is a pony cart you never have to feed or worry about tearing up the floors. Purify Food and Drink can make hundreds of pound of food and thousands of pounds of water safe to consume.
Animal Messenger can send messages 50 miles for essentially no cost. Magic Mouths can be used to disseminate information in public places. Skywrite can disseminate information to entire cities. Augury helps people make fewer bad decisions.
Waterbreathing changes ship repair, construction, and even allows mining in flooded caverns. Water Walking can make boats or ferries irrelevant or result in a horse-drawn boat. Phantom Steeds provide a version of the pony express that would kill horses.
Using spell slots, Goodberry can feed/heal 10 people. Continual Flame is worth it for mines, anyone underground any long lived race, places that needs lamps for hours every night, and places that are fire-prone like ships. (The cost of light has historically been a huge factor on economies)
Plant Growth only needs to be cast once per year to double to production of 500 acres. A priest working 5 days a week, 45 weeks a year can make
112,500 be twice as productive.
Wall of Stone, Stone Shape, and Transmute Rock+Move Earth would result in fantastic architecture and incredibly cheap bridges and defensive structures.