At what level / IV perfection should we power our Pokemon? [closed]

so we know each Pokemon as a level and an IV(Indivudual Value) which determine CP. You can learn more here : https://pokeassistant.com/main/ivcalculator

What I was wondering is, at what point should we consider powering up a lvl 20 Pokemon (from an egg the max lvl is 20) to 30 (which is the max lvl for wild Pokemons). The rarity, IV % and moves are certainly some factors.

For example is it worth powering up a Dratini with 95% IV perfection from lvl 20 to 30 ? Or should you look for a wild lvl 30 with less IV % ?

I'm not especially looking for a concrete answer, except if there is a tool somewhere, but rather for answer pieces.

This is my opinion (because this question is opinion based):

One key is patience. You'll probably get a better Pokémon once you powered up another one. Do not power up early, unless you have a perfect Pokémon with good moves and good IV. And even then you could get an equal one with higher level.

When you're good to go do it this way:

First thing to do is check the moveset. You don't want to keep Pokémon with bad moves (no STAB, bad ATK, ...). Even with 99% IV it's no help, if your attacks make your opponent laugh. Then you should go for IV, but that's not always the key.

With rare Pokémon where Candy are hard to come by you should look for high level Pokémon and power up these, if the moves suit you. High IV are great, but if you run out of Candy you might have to wait for a long time before you can use that Pokémon properly.

Common Pokémon or those where you have enough Candy you can safely look for Pokémon with good IV and power up those.