Thanks everyone for the input, I really appreciate it. I plan on getting a female spider or pastel. So that would make to bp in my collection. I think I will be getting a rack for these two reasons:
1. A four slot rack would take up less room than two tanks. Even if I only get one more, I will save on space.
2. My bp does hide all day except on feeding day anyway.

I don't mind cleaning a second tank but two tanks would take up two much space.