I couldn't tick one or the other of the boxes – I think the choice has to be made contingent on so many variables. In fact we have painted timber, double-glazed bifolds (with a fabulous retractable pleated fly-screen) at the end of the dining room leading out onto a terrace and a painted timber, double-glazed slider (with a timber-framed sliding fly-screen) on the other side of the kitchen (but on the same axis) opening onto a raised timber deck. Each works really well in terms of function and aesthetics but they would not be interchangeable as the different locations determined which was more suitable – but they have been made by the same highly skilled window craftsman and have given us nothing but pleasure. And on a hot, steamy evening with both open we have the most wonderful cross ventilation.

Wow I too have the same glass above my doors. Mine are all internal swing doors therefore I don't have your delema. I'm in the middle of renovations and mine are staying. My walls will be dark and modern with all the trim white with the original character and it looks great. With your wall, it's a lot to deal with therefore would suggest replacing the slider with a glass door with timber trim, keep your walls light modern and bright and paint your trim dark (any colour you favour) here is my example to give you an idea of what I'm talking about hopefully you can see the value here is a snippet of my renovation good luck....hope my idea gives you plenty of ideas

I agree that you need a blind like a roller or roman that goes up and out of kitty's way. Nobody has yet addressed your query about panel glides: Panel glides work best on large doors where there is room to stack the panels when opened. you will lose at least one third of your left glass door panel if you use panel glides and they also project into the room quite a bit.

If it is bare particleboard then my short answer is probably no, it is not worth paying double for better quality doors. Like I said, I haven't seen unfinished particle board inside cupboards in a long time. If it is laminated particleboard then it might be worth it. Like The Joinery Store said, laminated interiors are typical. Plywood is not unheard of (and I think it is more common in some other countries) but it would be unusual if you did not specifically request it. Just to be clear, the cupboard has been built and has laminate doors, and you are getting quotes to change the doors? For what reason are you thinking of changing them? What do you want the doors to look like from the outside? Do you want them to match any other doors or features in the room which are timber or poly?