Changes

Now in this example you could use all your Dratini candy (+ stardust) to power up the Dragonite, but in my opinion it would be better to save the candy until you have enough to evolve the Dratini into a Dragonair, because chances are that your newly evolved Dragonair will be stronger (i.e. have a higher CP) than your vanilla Dragonite. All without spending any stardust.

Keep in mind though that these decisions are always done within a snapshot. By which I mean that you could find a pokemon with a lower curve but higher CP when you’re a couple of levels higher. So try to remember which pokemon is caught at which level, but in general I wouldn’t worry too much if you keep your pokemon list clean (i.e. transfer the ones you don’t use), since you’ll probably know with one you caught last.