Apple should buy. Apple has no foot in cloud services. They should get rid of iCloud and buy Dropbox. This will give Apple some ground in the cloud services
If it didn't make sense for him back then why should it today? If I'm not mistaken they're profitable so they're in no immediate need to be acquired.
The only part that compares really is iCloud Drive. It could be improved (what can't?) e.g. it's not always super fast to show updates on other devices, but honestly it's not enough of an issue for me to use another storage solution.