I looked into the KQs, and it said that the stat goes to a random pet, not necessarily your main pet. Is that still the case? Because if so, I'll definitely pass on it.
I have bought nc once, and that was to get the extra ten pet slots on my account, haha. Definitely don't need a random stat I paid for potentially going to (once I get a couple more) one of sixteen pets!
Currently I'm on 5 codestone training (funny enough, I paid a lot to drop my str after a random event put it to 201, then got two blasted battle faerie random event quests in a row that bumped it back up. Just my luck!) I've currently got a small enough stack of codestones, mostly via random events and the battledome, so I've been working through those and not looking forward to when I have to start buying them.
I normally hope that I can get the bank bribery boon, or failing that cartographication.