Should I keep powering up my Dragonite?

Dont do it , because you maybe find Dratini with good IVs in the wild or even hatced one .. I have Dragonite with same IV and same moveset , I power him up to 26++ before the update , after the update it become 27++ ..

Power it up till it suffices to stay in the gyms in your area, but don't waste candy for more

You only have 20 candies. Wait.
Anyway this dragonite is not worth powering, bad moveset, low iv, low cp.

Power up to 2500, and put him in gyms. Then prioritize getting a new one with higher iv :)

Appraisal only above average? No way. Just use him as an attacker and save the candy for when you have the ideal defender.

I regret powering up my first Dragonite with 78% IV's (and he even has the best defensive setup Steel/Pulse). Now I'm sitting on 9 Dratini with 89%+ IV's and nowhere near enough candy to evolve + level them.

Remember, every time you power up a Dragonite to 30 you're pretty much giving up an evolution on another Dratini plus a bunch of dust.

First question is for what purpose do you want to use this Dragonite. You suggest you don't understand movesets but the website you are posting this on has profiles of each pokemon that you can check 'best' attacking and defensive movesets. Once you've figured that out then the next question is do you have access to Dratini spawn points i.e. are you likely to obtain more Dratini candy. If so in a big way then I actually would suggest you may continue powering up to 3K and shove it in a gym for position purposes.

That's pretty rough man. That's the only moveset I don't like on a dragonite, steel wing is pretty bad for attacking and hyper beam is pretty bad on defense.

If dratinis are really rare in your area you could just power that one up as an attacker and let hyper beam carry you or let steel wing carry it as a defender. Or you could grind 100 more candy and roll the dice again...and then grind candy to power it up.

Don't let ivs impact your decision too much. Rarity, moveset, and your circumstances are more important. I brought a 51iv(about the same as yours) to 2950, it has the right moveset and it's not worth my time to grind 125 candy for chance to roll a another perfect moveset with only 150 or so more cp.