I'm concerned that errataing some but not all things might make already sketchy cards like Fevered Visions and Guttersnipe even worse than they already are.

There will always be corner case awkwardness, but with each year, those will be less and less of a focus.

Do you as a designer ever want to create cards like this hypothetical "Vanilla Noncreature Spell" to see if someone can effectively utilize it? Something along the lines of a 0 cost Vanilla Instant in a set with cards like Guttersnipe, Young Pyromancer, Monastery Swiftspear or even Kiln Fiend could be a bizarre but interesting tool.

The problem is it takes up space that can be used to make a card that significantly more people will play with and enjoy.

could a creature-light set be done if the creatures were crutial to use alongside the spells, perhaps with things like guttersnipe, goblin electromancer typed affects finding their ways into any color? if the sets around were heavier on creatures than usual, would it be able to work?

The question isn’t “Could I make a creature-light set?” but “Should I make a creature-light set?” I could but I shouldn’t. Note that this doesn’t mean we won’t ever make it lower than normal but lower than normal and creature-light are not the same thing.

What guild is Guttersnipe actually from? I am very conflicted between it being Izzet or Rakdos.

It’s mechanically Izzet but creatively Rakdos.