Using the 24-105 at the wide end using manual focusing for landscapes/architecture is also a good idea. Drop the ISO down to 100 to maximize DR/sharpness and stop down the aperture to f/11 or f1/16 to maximize DOF. If you are ok using this workflow for landscapes and architecture, then the TS-E will be a great addition for you.
I will play around this weekend MF no-IS with my 24-105 and see how i get on... good advice, thanks!
The only problem with F16 is that its diffraction territory and softens the image... F11 is as far as I would go...
Diffraction softens it somewhat but it does extend the DOF. If the lens needs a few stops from wide open to get to the sharpest setting, then the diffraction softening at f16 may be worth the additional DOF (it may be sharper at f/16 rather than wide open). See lens rentals column below.