bejacob's provided the succinct (and correct) answer. But to expand slightly, this question is raised every now and then, and whenever one of the MRI moderators passes the question on to the team at MRewards, the answer comes back that promotional certificates have neither a cash value nor a points value; thus, they cannot be combined with either cash or points for a night's stay at a higher-category property.
I agree with others who have already posted comments. However, there are genuinely good Cat. 1-5 hotels available for E certificates
I'm staying at the Augusta Marriott (Cat 4) using E certificate this coming Friday in preparation for my 55th high school reunion nearby. En route, using 35k reward points to stay at JW Marriott in Atlanta-Buckhead, a wonderful location for nearby shopping, restaurants, concierge floor amenities, etc., and staying here nets us 100 miles nearer to Augusta for our trip.
Highly recommend both for those who might have opportunity to stay in these areas in near future!
Most desirable hotels in the Northeast are at least a cat 6. There are a handful of 5s left but far and few between. The fact is, if you want to stay in Philly, NYC, or Boston you are going to be out of luck looking for cat 5 and below. Sure there are some properties outside the city limits but the whole point of a trip is to not spend it going to and from the hotel because you have to say 20-30 mins outside the city to find a hotel at the right category level.
Come visit me in Columbus, Ohio. Of the roughly 23 properties in town only 1 is category 7 and 3 are category 6. The rest are 5 and below. I will admit, there are only 2 full service properties (both Marriotts) in that latter group.
Even better, about half the properties in town are category 3. Nothing fancy, but what would you expect in a medium-sized Midwestern city?