Besides replacement, how do I spiff up hollow bedroom doors?

Add Moulding or Moulding and Wallpaper/paint or Door Vinyl decor etc...

I love these ideas, and plan to use some myself soon:

https://www.remodelaholic.com/update-flat-doors-bifold-doors/

https://www.hometalk.com/diy/windows-doors/doors/hollow-core-bore-to-a-beautiful-updated-door-diy-slab-door-makeover-15862926?expand_all_questions=1

Hi Grammoe,

You can add molding to your doors to update them, then paint. Click below to read how a couple of other Hometalk members updated their doors. Wishing you the best.

https://www.hometalk.com/diy/decorate/rooms/how-to-add-trim-to-plain-bifold-doors-27555118?expand_all_questions=1

https://www.hometalk.com/diy/bedroom/closets/upgrade-the-look-of-your-flat-doors-with-this-simple-diy-28507123?expand_all_questions=1

Depending on your skill set and budget? You can get a wood veneer and contact cemeant it over your existing door once you’ve taken off all the hardware and handle!. You can use whatever species of wood you like? Maple, Cherry, oak, walnut, etc! If you want to stain and lacquer or varnish the door. If you want to paint use birch veneer if your existing doors are in bad shape? If you don’t mind spending a little more money and want easy to clean doors! You can also use laminate on the face of your doors too! They got wood looking materials and every color or pattern under the sun! There are 3 basic brands of laminate. Wilsonart, Formica, and Nevermar . Each brand has their own colors and patterns that may differ from the other brands! As long as your not adding more then a 1/8” to your door your hardware should all still work. I haven’t had one yet I couldn’t use the same hardware with! If your wanting to give your doors more depth? If you can find the right size kitchen cabine doors that you like you can glue them to the face of your door too! Then stain or paint to match your door or be bold and paint a second color! Whatever fits your fancy? There’s no wrong way long as you like it! The heck what others think, your the one living their looking at it day after day! So make it how your the happiest! Best of luck!

I replaced all of my Luann doors with six-panel doors over time because I think they look classier.

There are lots of ideas here: Home and Garden DIY Ideas | Hometalk

You could also experiment with washi tape to get an idea of what you'd like to fashion on your door.