I don't recall seeing any sources of what von Spee's actual best speed was at Colonel. HMS Kent did run down the Nurnberg at The Falkland Islands, but Kent achieved 24 knots, a full knot faster than her paper top speed. I remember reading somewhere that all the the non-essential crew were standing on Kent's stern to get every last fraction of a knot. And then Nurnberg had a machinery casualty that took her down to 19 knots. This implies that von Spee was not much slower than his "clean" top speed right out of the dry dock, despite being at sea for so long.
This is important because von Spee is not going to accept combat with a battleship, and if he is able to control the range by being faster, the battle does not happen. Craddock will have to run away from his battleship or sit and watch von Spee get away.
So like you say, then the deciding factor really is how much coal von Spee has on board. If he needs to so to South America, then he may get bottled up as you say. If he can dodge out into the Pacific and meet with his colliers as historical, then he can coal at one of the remote pacific islands like he did.
I am stuck on the dull idea that too slow is too slow, and all the pre-dreadnoughts are too slow. Likewise a battleship is a battleship and the armour and 12" guns make them all so deadly and hard to kill for an armoured cruiser that they are interchangeable. I do agree that Canopus turned out to be a spectacularly bad choice, but I don't think there is a good choice.