I have both the 1DX and 5DIII. I had the grip for the 5DIII, but I have sold it. I use the 5DIII either when I want something smaller and lighter or when I shoot low ISO, manual focus (TS-E or Otus), often on a tripod, with RRS L-bracket. For everything else I use the 1DX. The grip was collecting dust for a number of months, so I sold it. No regrets.
That's sort of what I was thinking, too. I foresee the 1D X becoming my primary body unless I need
more megapixels or a smaller camera and in both cases, I think I can live without the grip. I've got it and the RRS L-bracket, so that's a fair amount of money tied up in something that isn't likely to see as much action going forward.
I like my 7D with grip, wish I'd done it a long time ago, I like having the controls for portrait orientation. However due to the flexibility of the battery grip it is advisable to remove it for tripod work so if your landscapes will be taken from a tripod ditch it, if you hand hold your landscapes it becomes purely personal preference.
Not much help maybe, but just my thoughts on it.
Graham, I appreciate your feedback as well, and I really like gripped bodies, too, and have had one on every model I've owned with the exception of the 5DII (I'm not sure why I didn't buy one). Now that I have one with a grip built-in, however, I'm questioning the need for two large camera bodies.