Rare candies for Dragonite

No. Find a better IV Dragon. Right now, With legendary raids being most popular, Dragonite as an attacker isn't very prominent except as a generalist. Save candies for the birds. After Zapdos, we might get legendary dogs also.

what level is the dragonair? if it is level 29-30 might be ok.
how common are dratini in your area?
how easy is it to raid for candy?

in my area I wouldn't if it was level 29 or 30 i would spend dratini candy if it was lower i wouldn't bother. There is a good chance that dragonite will eventually become a raid boss as well giving you more chance as much better placed dragonites.

I've used some of my extra on Abra (20) and Larvitar (10) so far. I have a large enough stock to take 3 legendaries to Lv 30 though and defeating raid bosses isn't too much of a problem (catching them however is another story), so I know more candy is coming.

Using over 80% of your pile seems a bit steep though.

Yeah, too low IV on the dratini for me. Wouldn't stress it really. Everyone is expecting Dragonite to become a raid boss soon, so you'll be able to catch a good IV one then. But then again, it's up to you :) If you have lots of candies and don't wanna spend it on legendaries etc, then go for it.

No, there should be some Dragonite raids in the near future.

I have a 100%IV Dratini and not even evolve it. Just save the rare candies for the legendaries. But feel free to play it your way.