I've done landscape photography with both Canon 7D (APS-C 1.6 crop) and a Canon 5Dmk2 (fullframe). These are my random thoughts:
APS-C is best if you want a lower cost and/or lower weight system, and don't think you need more *effective* resolution than 12-16 megapixels. The 7D has 18, but it does stress the lenses resolving power so at pixel peeping level it may be quite soft. A bit over-resolution is good though since images respond better to upscaling (no aliasing) and deconvolution sharpening, just don't expect that a 24 megapixel APS-C will deliver as sharp pixel-peep images as a 24 megapixel fullframe.
Then preferably use the best APS-C specific lenses. Nikon has a wider range of quality APS-C lenses than Canon, but there are also some good Sigma lenses. The advantage of APS-C specific lenses is that due to the smaller image circle they can often be made sharper than a fullframe lens - sharper meaning that smaller pixels can be resolved, the best fullframe lenses still wins in total resolution when resolving over the full frame. The advantage of using fullframe lenses on APS-C is of course very low dropoff in the corners, but then center resolution is often lower than on an APS-C lens.
I'd say overall it is more about lenses.
The Canon 24mm TS-E II can be a strong enough reason to choose canon fullframe as a landscape platform both due to its very powerful movements and that is is very sharp (for being a 24mm lens). When resolving power is as high as it is today I think tilt starts being valuable. Shift is also valuable for composition, especially at wide angle. To go wide-angle tilt-shift with APS-C you need the 17mm TS-E, which is more expensive and less sharp than the 24mm TS-E. For wider than 24mm it does seem that for APS-C you'd want dedicated APS-C lenses, fullframe ultra-wide lenses don't perform that well on APS-C. On full-frame I don't go wider than 24mm. It is a matter of taste, but I think wider than 24 gives too much perspective distortion in most cases. With full-frame you can get weather-proofed lenses, as far as I know not any of the APS-C lenses are.
For full-frame I'd suggest using primes, 24, 35, 50, 85/90 and then the 70-200/2.8 zoom. The 70-200 is probably the best performing zoom lens there is. For Canon the 35mm is the weak spot, actually I think I prefer putting a 1.4x TC on the 24mm TS-E (or take the shot with the 24mm on the 7D). 50 - 100 mm primes can be bought both cheap and very sharp. On Canon, TS-E 90mm is very sharp, unfortunately the TS-E 45mm is not as good.
Fullframe is future proof to at least 36 megapixels I think, while APS-C has already approached suitable maximum resolution for what current lenses can do. Fullframe has also a stronger tilt-shift offer. The fullframe system will be considerably more expensive and heavier though. There will be more problems with dropoff of resolution in corners on fullframe, but overall you can get higher resolution out of it. Even if you don't think you will use tilt/shift much, on 24mm it may be wise to use it anyway due to the larger image circle and therefore better corner performance.
Currently Canon has a stronger tilt-shift offer on 17 and 24 mm, while Nikon is better at 45 and 85/90 mm. Having a Canon system you can use Nikon lenses though with adapters :-).
The importance of having tilt-shift is much about shooting style. I've got used to it, I think it adds another dimension (and helps improving technical quality), I use it all the time and don't want to be without it. Those used to tech cameras probably could not either, but many do shoot landscapes with great success using just 24-70 and a 70-200/300 zoom. If you're the zoom kind of guy and are not too crazy about getting the sharpest possible images a D7000 with zooms, perhaps sigma 8-16, sigma 17-50 and something on the long end (perhaps a full-frame 70-200, they're really great on APS-C too, and you then can do some action shooting too) is probably the best alternative today.
