This is really a very personal thing with a whole lot of variables attached, but here are some things to think about, with some personal comments so you can see how they apply
Do you own enough points to use them to cruise AND use the points as you would like at Disney? Is cruising a priority over using those points at WDW? We only have 150 points, so I'd need to horde them for three years to get a cruise - skipping our WDW vacations. It was pretty apparent we'd rather use our points within
DVC - and pay cash to cruise. We get our cake and eat it too, but are lucky we can do both.
How do you value your points? Some people figure $6 a point, some people figure $10, the going rental rate. What would the cruise cost cash and is the difference worth the headache of renting out your points? Sometimes, when you do the math, its cheaper to use points. Sometimes its cheaper to use cash. Sometimes, the difference is so small in favor of renting that you are better off just paying in points and not bothering with renting. Sometimes, its so big that you'd need to be pretty cost immune to not think renting a good deal.
If it IS cheaper to use cash, are you actually going to go through the bother of renting your points to pay for the cruise? I suspect had I used this logic to pay cash for the cruise, I would have ended up not renting the points and taking two vacations - which is what we decided to do. I also suspect that cruising is a good way to start add-onitis.
Do you have the cash to cruise? We just booked our first cruise with some money we had lying around, so it wasn't a big deal. If you don't have the cash to cruise, sometimes paying in points works really well - that's paid for.
If you have the cash, would you rather own more DVC points and use some of them to cruise. I could have taken the $2500 it will cost my family to cruise, plus a little more, and bought more points - not nearly enough to cruise on, but a start. But we are happy with the points we own. No add-onitis for me (yet).
