I’m being plagued by the thought that nobody will use it.

If you don't finish it, nobody will use it. If you do finish it and nobody does, so what?

building it out would require spending some money and a significant chunk of my time

Working is the hard part of working on ideas.

I really don’t want to build something no one wants

Wanting to build something is the reason to build things.

I’d die of embarrassment

No you won't.

I’d just be sad about wasting my time

Inefficiency is the luxurious reward of creative work. Good luck.