Some great points being made here - for me, the two major things are how quickly/easily you can earn Marriott points, and I like the suggestion about the longer the stay the better with Marriott. Those two items add a lot of context to what your points are worth.
Getting X points per penny is a great calculation, though it is also true that if you are an earning machine, the calculation is less critical (doesn't mean it's less relevant, just less critical to your situation). Some folks here (not me anymore, unfortunately) seem to amass so many points that their reasonable ability to use them should probably be a factor - if you have half a million points or will get there, why not use them? Sometimes I think I spend too much time trying to figure out how to earn points and not enough time on how to use them - $150/night with taxes is not insignficant for a Cat 3 hotel - I'd be inclined to consider using points on that. I personally don't think having more points or miles than you can use within a few years makes a lot of sense, if you are spending real dollars today to bank points you'll use later, when redemption values may increase (they could decrease as well but when does that happen?).
However I also feel that the fact of points per night decreasing with each subsequent night with Marriott is a critical factor - the drop off in points needed night by night is significant and to my knowledge is a somewhat unique structure to this program on basic award charts. If a 7 night stay/travel package is in your future, the points might be worth holding - that 5th, 6th or 7th night gets pretty cheap on the points. We personally tend to use our points to stay in places we'd never be able to/want to pay for ourselves, like a $400/night resort - the value of using points for a longer stay like that, and having a luxurious stay you might not otherwise have is worth considering.