Would you eliminate stairs to add a bedroom?

[Seth Levey]

I have a large SFH with 3 bed/1bath/living room/kitchen upstairs and 2bed/1 bath/living room/kitchen downstairs. The downstairs is mostly above grade and has a separate entrance. There is an interior staircase connecting the two levels. At the top of the stairs there is a large foyer area that is large enough to add a bedroom if I fill in the flooring and cap off the stairs. I'm going to add two bedrooms to the lower level as well. Then I would have two 4bed/1bath units like it were an up/down duplex. It's actually zoned this way. I'm a little hesitant to change the layout of the house so much but I like the idea of the extra revenue potential. Good idea or more trouble than it's worth?