How would you spend 172 dratini candies?

I'd forget about those and lvl up your Crobat

Impressive line up to Dragonites! Man 3 DB/DCs.... sweet, despite their IVs! You seem to have quite a few that can be readily put in gyms or high enough CP to attack with, so I wouldn't do anything with those (2925-3146 CP ones). The SW / OR and SW /DC, I guess you can power up more if you need more defenders. You can even use the SW/OR as an attacker, but not optimal. Need more attackers, I would power up that DB/DC 67. The 846 CP one would be a lot of dust and candy expenditure to power up for me.

If you don't need any attackers or defenders right now, evolve that 98% and make it a project if it has a good moveset.

SAVE YOUR CANDIES!!!

I would try an evolution to maybe get a DT/O or H

Save candy for a level 20 dratini hatch

It depends how urgent and how much you need a very high CP dragonite as a defender (Don't care the movesets). For me 3100+ is decent for normal low level gyms, but it might be the different case for you. And also, do you want a DT/O or H attacker? If no, don't evolve it.

Don't be a wuss and just evolve that 98 IV Tini.