The Cook islands are a really wonderful place to stop over, many flight options allow a stopover on your way to New Zealand, I certainly recommend spending a day or two in these lovely islands if you travel plans allow.
I stayed for around 48 hours here and that gives you enough time to explore a little, I hired a moped and was able to go around the entire island in around 50 minutes.
The locals are friendly and if you are traveling in the European Winter then the weather will be delightful.