Official comment
@Ves > No, there are no discounts on the Professional plan.
Additionally, if you subscribed on the initial offering discount for the Core or Creative plans, those were a one-time offer and if you cancel your plan, you would not be able to renew at the previous discounted rate.
@Donnie > If you subscribe to the Professional plan, you are given the option to switch your Dropbox subscription to this unlimited plan, effectively cancelling your existing plan (and I believe Dropbox even provides a refund if you have subscribed annually). None of your music is lost as it would all be transferred to the new Dropbox account automatically (same email address).