Actually not.
Keep in mind that what's halved is sequential transfers. Random speeds are closer and are much slower than sequential. Large sequential transfers are surprisingly rare, and when they do occur, transfer time often isn't the long pole in the tent anyway. If you have a process that takes say an hour on the older machine, it might take 10 minutes longer on the new. Even assuming pure sequential reading, it would take about a minute and a half to read the entire 256GB with the old SSD and 3 minutes with the new; so whatever you are doing that takes hours isn't just I/O unless it's a remarkably poorly written process.
Bottom line is that in real life you will be hard pressed to notice; and if you think you might be the exception, you are likely to be buying the larger SSD's anyway.
Source:
So in real-world tests, the slower sequential transfer really is making a huge difference because that's what happens when you swap memory between SSD and RAM.