Everything Depends on your decorating style.

If you have something fabulous to display and you like a boho look, I would highlight the moulding with a Rub&Buff (from any craft store) Gold, Silver, Bronze... your 'metal' of choice. It's easy to 'polish' on a shimmer.

I'd personally paint the interior Flat Black.

In older homes, that is known an a coffin niche. When bringing a coffin up or down the stairs, it provided extra space so the coffin frame wouldn't damage the wall.

I don't think you need to do anything to it. Maybe put a larger sculpture or vase in it, or paint the ornamental plaster white to match the trim. But it's already ornamental.

Madonna statute.

If you don't already have one in your yard. Don't wanna over do a theme:

I would look for a taller vase and tall items to put in it. Nothing too heavy - a more delicate look. You may want to consider painting the inside a different color

Or you could hang something from the top.

Good luck!!

Elvis: in his later period. Or maybe "The dude". Here's a fine sample from Etsy: