Depends on your use case. or me, it's going to take many moons to get an extra $500+ of value out of a washing machine (probably about the time I was within 6 months of the payback-period is when it would give out, knowing my life).But they also do a lot more. Whether it's being a front loader and handling a larger load or has sanitary options like steam and UV or has better components and build quality? You don't think the $850 washing machine has a better motor in it than the $300 one? And that's just washers, same type things apply with dryers too.
Now I'm not saying that you should go top of the line but I certainly wouldn't go bottom barrel.