Well, I don't think "more powerful" is a good way to think about it. A spreadsheet is essentially a functional programming paradigm. One programming thingie is not going to be "more powerful" than another. That said, one could be cooler or more interesting than another one, at least to you.

My feeling is that it doesn't have to make sense, and you don't really need to have any justification. If you want to make a spreadsheet system with Lisp, I'd definitely do it. You learn the most when you do your own projects, and interest is the fuel.

Also, we're bad at determining beforehand what actually is important, so maybe you work on something as a toy, but later it (or some piece of knowledge developed while working on it) is crucial for something else later.