I think there are so many ccTLDs and nTLDs on the market now that it would be unwise to expect good investment value from adding a good keyword to [insert extension here].
.COM.CO is mainly for Colombia. It will be undesirable for branding purposes because it's confusingly similar to .COM and .CO.
So buyers with budgets for creating new websites will skip this domain altogether. Who does that leave? SEO types and domainers. Budgets are a lot lower.
If you get any inquiry -- regardless of value -- sell. Otherwise, don't renew.