First image is my last attempt and the second one was my very first so at least there was a little bit of improvement, but for some reason I can’t make the scene look realistic. I used a dome, rectangles, spheres, tried textures on furniture/floor/walls but it still looks pretty meh.
Any tips? 
I am by no means and expert… but there is a lot you can do. First I would find some reference images and try to match or mimic some of the things you like.
What is behind the viewer? Windows that can cast shadows and let in some color from outside? Is the scene morning? Mid day? Evening?
Why are the chairs all perfectly lined up and not a bit askew from one another? Some should be close to the tables, some further away.
Why is there nothing on the tables? Or the counter?
The back door to the left could be open a little bit.
The blue cushions could use some definition. Maybe some variation in texture or color.
Are you using ambient occlusion? You can use it as a render layer and then adjust in photoshop, or IIRC you can use it globally.
You can add ‘dirt’ to edges similar to ambient occlusion by adding secondary textures within your main textures and applying this to the edges, etc. Same with adding noise, etc.
There could be menus or other stuff on the counter.
The design overall seems cold and clinical, so maybe it needs some warmth, or some lights that drop over the counter from the ceiling to break up the space?
I’m intermediate at best with V-Ray myself, so I’ll do my best
So, you’re saying you’re using supplemental lighting to lighten up the scene? A dome light it outside, so not sure how much that does on an interior. Supplemental lighting on interiors is a really complicated and developed skill set. It’s hard to do well and still look natural. It may be there’s too much supplemental lighting such that the lights in the image don’t look like they’re doing anything. Light falls off with the square of the distance from the source, so there should be hot spots near a light source and shadows developing as you get farther away.
@eric-s is far more skilled at V-Ray than I, and particularly fond of it’s post processing tool for dialing up/down different light sources without having to re-render the scene. With that you could dial the supplement lighting down in post and see the effect as you played with it.
You should try adding some decals, don’t try to make it look perfect, what makes perfect a render are imperfections. I think your first image is better than the second one, imo the second one is overexposed, the neon lights have too much bloom and you can’t read what it says, just increase a bit the exposition to the first image, probably an invisible spherical light on the ceiling and lots of imperfections, there are some nice decals on the chaos cosmos library and you can model some more if you don’t find what you want.
I think you are confusing “realistic” and “good”. Both your images look much too bright compared to what that kind of lighting with a few opal glass spheres produces. I have used those in several projects where the historical milieu requires them, but to be honest, the result is bland. To produce, for instance, lighting levels needed in an office environment, the ceiling has to be practically full of them. So, if you put in more light than comes out of your actual luminaires, the result is not realistic.
I think that looks pretty good.
Can you share the SketchUp file, it’d be fun to have a try and see if I can make any suggestions.
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Yes of course! I will still be trying to figure out new settings 
I can’t upload the file here but here’s the WeTransfer link:
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