Good morning, looks like you are well on your way with your winter scene.
Modeling winter is a tough season to model due to the snow and ice and the way it changes the landscape. I have been modeling winter on every layout I have built and like you I am always looking for ways to make the scene on my layout more realistic.
One thing for sure, I strongly recommend that you do not put any snow flake material around the track area.
This material, not matter what you use will raise havoc with motors and drivetrain items in your engines. I keep all my snow material away from the tracks due to this reason.
As they say "been there done that", and what problems it made for my newer engines loaded with electronics.
I mentioned on another post if people would ask why there is no snow against the tracks, my answer is I only run steam engines and they either blew the snow back from the tracks as they went by or they melted it !!!!!
I do have areas of ice around and between the tracks but everything in these areas are well glued down.
Go to Woodland Scenics web site and search Winter Scenes and there is a complete video on making realistic winter scenes using their products. Even if you don't use their products there are some very good technics.
Looking at your photos I think you need some rock faces along the walls. Adding rock faces will give you all kinds of scenic opportunities from snow drifts, vegetation, ice and icicles hanging from the rock ledges.
Also as you will see on Woodland Scenics video you need to get rid of all the white and get some brown and green areas. Not matter how much it snows there are always areas that the snow is not as deep as others.
I made this mistake with my layout and ended up going back and repainting areas to show the bare ground and higher grassy areas where the snow was either blown and then drifted up against a fence or a building.
The lower corner you could build it up and put a frozen pond scene with possibly a waterfall coming down the inside of the trestle and flowing into the partially frozen pond.
All of these items enhance your scenery and give your layout that wow factor.
It takes time so don't get discourage, Good luck, and have fun !!!!!