may I use Marriott points to book a Regent Cruise/
Yes, you can but the points required is insane. Please find the chart below. Refer to the site - Cruises, Last Minute Cruises, Cheap Cruises, Cruise Deals, Cruise Bargain, Cruise Line for more information.
Many people use a valuation of $ .01 per point, (that was the pre-merge/pre-price change figure). A $250 room was 25K points. The point totals have increased, maybe 35K for a $350 room. Still the point redemption for a cruise is near double the points required. IMHO, not a good deal, but if your sitting with a million plus points, it may be worthwhile
To piggy back on what ks83 wrote, using points to book a cruise is possible, but it's not a good use of points. You normally want to find a way to use points that will yield about 1 cent per point. Using them to book a cruise gives you less than half that. Unless you're sitting on several million points with nothing better to use them on, spending those points for a cruise is a horrible idea.
I'd suggest paying for the cruise and earn Marriott Rewards points instead. Typically Marriott will give you 3 points per dollar spent on your cruise. Frequently they will run specials where you and earn double or triple that, especially if you pay for it using the MR Visa. I did this recently for a cruise of the Greek islands on Azamara Club Cruises and ended up earning around 40,000 points.
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