Hi mr. figment and Welcome to the DIS!
DVC should be purchased primarily for WDW vacations in order to get your best value. That being said, I have taken many cruises using DVC points, the most recent being this summer's Mediterranean Cruise.
The points can increase for cruises (and have), but have not drastically changed thus far. The types of cruises offered include 3, 4, 7 and special cruises such as the 10 and 11 day Mediterranean cruises. You can book them completely in points, or you can mix points with a pre-arranged DVC cash discount price. This price is usually somewhere between the best
DCL early booking discount, and the highest DCL rack rate.. So it is not your best price, but is fair.
As mentioned, some people will rent out their DVC points then use the cash towards booking the cruise totally on cash. I prefer not to rent, but it is an option if one desires.