I think it depends on how many children you plan on having, how often a guest room would be used by guests, what sort of time line you have for finishing the basement. I know for us, having 3, almost 4 kids, we need that bonus area as a playroom/family room. When we were looking at houses it was necessity. I wouldn't look at houses that didn't have a bonus area. But thats just what was important to me at this stage in our family. When we just had Lily and were thinking of
TTC Julia, we didn't need that bonus area at that point, so we didn't really have it. My parents do live out of town, so having a guest room has always been important to us as well.
I think it comes down to how often you plan on having guests, how large of a family you want, and how long it will take you to finish the basement.