How can I reuse vases?

Paint, mod podge.

Paint with one of many paints available for glass which you then bake to make dishwasher proof. Instructions are on all the various paints such as Americana.

Spray paint first and then glue pieces of vintage costume jewelry to vase in a pleasing design....

Glue glass marbles (the ones with flat sides you can get in the hobby store) all over and then spray with clear spray paint.

Glue bits of broken tile, china, pottery, etc. and then spray or Mod Podge.

Glue buttons, rocks or other interesting, fun things after spray painting....then modpodge or clear spray paint. :)

Use glass paints to change colour.

Stick on string around it to your desired effect.

Etch it. You can buy a spray.

Mosaic it. With tiny tiles, and grout.

You could give them the look of mercury glass. Here is a great tutorial... https://www.hometalk.com/diy/decorate/rooms/diy-transform-plain-glass-containers-into-embellished-mercury-glass-6983989