Yes, you can use points and cash to book a cruise. At least one adult in the cabin must be booked for points. You can choose to pay points or cash for the others in the same cabin. (You can't pay a combo of points and cash for the same person, though).
If you pay cash for a person, it will be the cash price that
DVC previously negotiated with
DCL. That price may be more or less than the cash price available from a
Travel Agent or DCL itself.
There is a fee (either $75 or $95, can't remember) to book through MS regardless of how you pay. You must pay the entire amount up front when you book through MS.
As far as whether or not it is a good value, that just depends. Take a look at this thread for more info:
http://www.disboards.com/showthread.php?s=&threadid=516922
Best wishes -