I have minor imperfections in my fixer upper. Don't intend on re-drywalling.
What's the best way to re-paint & cover imperfections?
Paint basically does not cover imperfections at all.
Even with fairly "thick" (high viscosity paint), I would guess it would take at least three coats to even get a thumbtack hole filled in, and you'd probably still be able to see an indentation in the wall.
Depending on the size and nature of the "imperfection", you might be able to use spackle or skim coat. There are some primers on the market that can supposedly cover very small imperfections (like a scratch from sanding) but I'd be skeptical of that.
You can't cut corners here. It takes practice (and early on, lots of time and patience) to be good at applying it. You'll have to sand it afterwards. Use a flashlight and shine at an angle across the wall, and fix any bumps, ridges, etc before you prime or paint (it's significantly harder to fix after painting as you're basically starting the process over).
Paint with a sheen (matte, satin, semi-gloss, gloss) will tend to make imperfections more obvious, whereas dead flat paint will tend to make imperfections harder to see.
You could apply a spray texture prior to painting. That would cover minor defects but requires some special equipment, materials, and skill.