Best use for my final few Dratini candies.

I'm in a similar situation. I've got 3 good lvl30+ Dragonites each with a different charge move. I had about 50 Dratini candy left and i'm just gonna save it for now and power up only if the need arises

If you got any shiny dratini that would be a great use. Got two shiny male/female both with Draco meteor that’ll be perfect for breeding

Reviewing the dragon training guide here, I think you could first save the candies for future unless you are desperate for a dragonite army for raid/gym battle. However from my experience I think your current mons should be enough as there are always superior options for any raid boss.

For me I am only having one Lv37 DB/DC and Lv36 DT/O dragonite for battle use. I did evolve one Lv20 with DT/DM but I am not considering power it up - same reason as the dragon training guide and despite of resources.

I would recommend saving it unless you have plenty of stardust.

If you really want a dragon army, power up one of the Dragonites you already have (assuming better IVs than your Dratini) and power up a Salamence and a Rayquaza. There are even more dragons coming in future generations so I am not spend too much maxing multiple Dragonites.