A sealer is often used on stone tiles as a grout release - prevents the grout from sticking making it easier to clean up. However, on tumbled stones with the rounded edges it's pretty hard to use a grout release. If you get it into the seams the grout won't adhere well. If you don't want to fill the holes (I would fill them as they collect dirt, especially on a backsplash) just grout carefully and clean up any excess grout as you go. I have had success keeeping a spray bottle of water handy to flush out any grout that does get in the holes.

I think it depends on context. The "Tuscan" kitchen is dated. Marble has been used in kitchens for thousands of years. Use a different shape or size than the trend (i.e., not 4"x4"), with different details in the rest of the kitchen and it'll just be what you like rather than a datable look. To me, "dated" in kitchens means something that you can pin to a particular style that was being shown and installed at a particular time. Kitchens last a long long time. "Dated" in the bad sense is when you can still obtain something that was really popular 10 years ago but isn't being done anymore. That is, that you'd be doing a 2000 kitchen in 2010. It's okay if a 2010 kitchen dates to 2010. Your appliances will give you away anyway. But you want to avoid the near past to keep from being just out of style. There's now, retro, and never was (i.e., unique rather than following a design trend). Dated is the gap between now and retro. What's a now look? Mini-brick! So go for it, match your fireplace, let it look good with the granite, and be very happy knowing you're in style.

We had a tumbled marble backsplash that we DIYed at our last house. I didn't find it hard to clean but we sealed it and I think that makes a huge difference. I found the seal seemed to wear off the grout faster than the tile making it harder to keep clean. This time around I wanted a more solid one-piece backsplash, but DH still wants tile so we will see what happens.

I do not like this white spot, either. I do not think you are being unreasonable to want to fix it. I think that we are just trying to help you think about other solutions. My first experience with stone was my 2003 kitchen remodel. tumbled marble. I remember looking at the finished backsplash and thinking why didn't my contractor set aside those dark ones that popped up every once in a while. After all, I had three boxes of tile left over. To me, it seemed a no-brainer. I also had no idea there was this much variation. But my contractor did. He knew what the tile looked like and how much variation was there. To him, the dark tiles were not something undesirable, or even something to ask me about. He had more experience, and I had not looked through the tiles to see what they were all like and pulled out the dark ones. Come to think of it, I helped him do tile on the second day. I put extra mastic on the back of the tiles that needed to be set forward a bit. On that day, I did pull out some tiles that were "too dark" for my taste. My expectations were different from Jim's. Now I am doing a second, different kitchen. I have an island that will be topped with 19" porcelain tiles that look like stone. I know from watching HGTV that some people lay tiles like this with no thought to the direction of the streaks of "grain" in the color. I hate that look. SO I am taking off a few hours on tiling day to give my input on the placement of the tiles and cuts. I would not know to do this if I had not seen other tile jobs I did not like, or see the dark tiles on my old backsplash. Since the sealer wears off in time, and since it is a liquid, I bet it has a solvent that will remove it. You may be able to do a "faux" finish on the white spot, then reseal it. It is possible that taking out that tile could hurt your wall and mean that the whole thing has to come down. Try something else first. After Bill Vincent jumps in and gives advice. There is a thread here somewhere about people hiring painters to faux finish outlet covers and other obstructions so that they cannot be recognized and ruin the flow of the backsplash. I would try that before taking out a tile and risking tearing the paper off the drywall underneath. Here is a link that might be useful: Painted outlets