Seems like your concerned about the 4x36 benchtop sander. Whether it can do what you'd like it to do. And really don't want the expense of the 6x48 benchtop belt sander. I'd ask myself, what do you want to sand with it... Then purchase accordingly.
I got my Craftsmans 4x36 sander, new in 1995. It did everything I asked it to do. And I wore it out the, 4x36. Gave it away to one of my step-sons, he's still using it. The reason I went with the 6x48, I make Memorial Urns. I do a lot of sanding, 5 1/2" to 7" wide pieces, from 5 1/2" to 8" long. I thought the 6x48 benchtop sander would handle them quicker. Verses my V-Surface Drum sander.
Sometimes you may feel the need for: Detail sander, 1/4 Sheet sander, 5" or 6" Orbital sander, 3"x21" or 4"x24" portable belt sander and 4x36 sander or 6" disc sander.
You may find all you need is the 4"x36" sander with 6" disc & a 4"x24" portable sander for the larger panels of wood, plus the Detailer Sander. This combo of three sanders worked fine for me (15 years). I didn't start getting the larger tools & sanders till I retired.