I would keep them but make them rituals. ...
Make as rituals but you must be this level to cast it. ...
Some of these should be rituals in my opinion. ...
Ritual is a great design space.
Many concepts that make bad spells, actually make great rituals.
I want to see 5e develop the ritual design space, separately from spell design space.
For example, any character can attempt to perform a ritual. A ritual can use an Ability Check to perform successfully.
The school of a ritual might correlate with a skill.
School of Ritual (Skill)
• Abjuration (Medicine)
• Conjuration (Arcana)
• Divination (Religion: Celestial or Fey)
• Evocation (Nature)
• Enchantment (Insight)
• Illusion (Deception)
• Necromancy (Religion: Fiend or Shadow)
• Transmutation (Survival: Earth, Plant, or Animal)
The more difficult a ritual, the higher the DC. There might also be a hard character level prerequisite, so certain high-level rituals are unperformable until a character reaches a certain level.
A successful Ability Check means one performed a ritual correctly.
Interestingly, a critical failure during a ritual can mean something goes wrong. This trope of forbidden magic harming inexperienced dabblers is something D&D 5e doesnt explore. But a ritual design place is a great place for these tropes.
A ritual can be anything, for anything, with any kind of requirement to perform successfully. A ritual can be for something routine, like lighting magical streetlamps in a city, or can be obscure like that one time one really needs a Hallucenary Terrain (LOL!).
While some spell effects also have a ritual with a similar effect, spells are not rituals. There can be many rituals that are not spells.
If a spell mentions a corresponding ritual, it can also mention the DC necessary to perform the ritual successfully. Any character can try to perform the ritual, whether a Wizard or a Fighter.
Rituals are a great magic item that DMs can hand out as treasure. The obscure ones can be flavorful. Some rituals might even be useful.
Many things that are currently spells are things a caster will never prepare. But if rituals are separate from spells, then there are many spells that are terrible spells but fantastic rituals.