It must depend what you cook. I don't do fried, spitty type dishes and the grout around the largish tiles in my now 10 year old kitchen is as good as new. I rubbed car wax into the freshly laid grout lines, same as I did in the bathroom. It also depends on how much light bounces around your kitchen, glass being so reflective shows up smears with light on it. Just above the kettle in the first photo is a good example. Each to their own, I'm a non-glass girl whenever I can get away with it.

I would get in there to enliven up the space without taking away from the clean lines. You don't do that by repeating more of the same. You make the rest of the kitchen, with all its weight and clean lines play into something not the same. I would suggest you look at a gold leaf look ( ie with a little texture in it. Obviously not actual gold leaf) and put the most vibrant magenta pink/red that you dare in a horizontal line about 2 inches wide and going the full length of the area. Just very well executed paint. Make it above your average pot size so it does not disappear behind pots and pans. That way every time you will look at that place in your home and think Oh Yeah! Also, if you would rather .... make the coloured line turquoise.

Mirrored glass is just as easy to clean as normal glass. Back-painted glass adds colour to a room and can look very sleek and modern. Mirrored glass can be dramatic but remember that it doubles everything that you have on the countertop. If you are a minimalist, you might find that more than you can take. If you put a lot of stuff on your counters, it could be overwhelming when doubled.

Hi, since your kitchen is small and there's a lot going on I would go with a very light coloured back splash. A very light warm grey as suggested could work nicely here. It would also brighten up the area a little. I certainly wouldn't introduce yet another colour. Introducing something like a bright red will draw attention to the backsplash area, but the design of the kitchen doesn't lend itself for such a high impact visual focus. Keeping it calm and neutral will make the kitchen look more like a unit rather that bottom and top cabinets with a big red/black/maroon stripe through it. The company supplying the back painted glass should either have a range of available colours to choose from, but usually any standard RAL colour should be available at a minimum. They will most likely have the RAL standard colours fan available for reference as well. I'd go with the one of lightest warm grey shades that is in the standard range. Your worktop has warm tones in it, your wall is beige, going in with a cool grey will make each colour look "off". The last thing I'd recommend is black. I know it has been mentioned, but it is just too strong of a contrast and non of the other materials and colours would support such a stark, contemporary choice. If you are worried that the existing dark red paint will alter the colour of your new glass back splash, and that's a very valid argument btw, just paint it over with two coats of white prior to installing the new back splash. I'd do that a few days prior to installing the glass to make sure the paint is nice and dry. In terms of maintenance a glass back splash is probably the easiest to look after since its so easy to clean and there's no grout that can attract dirt over the years. Good luck with the renovation :)