Hi! Posting my 2c here. When I moved into my new house a year ago we replaced the VERY old top loading w/d with a front loading LG from Best Buy. It was about $740 or so for each, and we had a coupon, I think.
It saves a lot on energy costs, and detergent costs! I used to use a full dose of regular detergent with the old w/d, and the new High Energy detergent requires only a tsp! I still can't believe how one tspn cleans a whole load. Plus it uses a THIRD of the water of a top loader. Definitely adds up.
As far as the vibration and the house, I have my w/d on my first floor, and no one told me about any danger. Keep in mind, I only use the MEDIUM spin speed, as I think the high speed is ridiculously fast and loud. So, I am sure that may help with the shaking. But, I have to say, that whole "watch the shaking of the foundation" thing sounds like hooey. My mother used to, for years, live in a beautiful, 150 year old triplex on the bottom floor not more that 50 feet from train tracks (obviously MUCH worse than a little washer) and there was no problem with the house or it's foundation or anything of the sort. She owns the triplex and has never seen any cracks or loosening. Maybe it depends on the house, but I there are plenty of new construction homes with laundry on the upper floors and I don't think the house suffers.
Anyway, to sum it up, front loaders are well worth the $ up front as you will save a lot in the long run. Yes, you have to leave the door open for a few minutes on the washer, to prevent mold, but every washer is like that. I do it, and don't even notice it any more..and it's only for five minutes. Hope this helps, and good luck!!