removing the door to kitchen would be easiest & cheapest way to open up & brighten the hall area. Next best, but more costly would be replacing door with one with glass panels. Look for used one in 2nd hand or @ your local Habitat for Humanity store. Keep the one you take off just in case other one gets damaged and needs to be replaced. Replacing only two panels would not achieve much I don't think. A mirror should only be placed where it can reflect something of interest & expand the room. If I recall, the staircase is what would be reflected? A photo collage frame? I think more colour is called for here. Your home, your choice. Bottom line is you decide what is right for your space. As you have likely noticed everyone has a different opinion, professional or not. Most important in re-styling a space is what the home owner wants to use the space for & to be their taste.

A niche would be a good way to add some drama without infringing on your circulation space. It doesn't have to be deep to be effective. You can do one simple vertical rectangle, and line the back with a mirror, or add some colour with paint, wallcovering or wood. It would be great if you could also add a recessed light fixture at the top. The attached images are perhaps too busy for your situation, but it gives you a good idea of what can be done. Good luck!

Paint the doors black matt and the fames cream add silver crome door furniture. Huge silver mirror above the covered radiator then add a runner of any colour you like and match it with the lamps and lighting. hey presto done.

Hi Odette! Have you had any progress with decorating? Hanging a mirror could be good in terms of light reflection and making a space seem bigger than it is. I like your idea with the photographs and horizontal lines - I might add some adjustable spotlights to make a feature out of the photographs! For e.g.