One advantage of the 24 TS-E is its relative lack of vignetting, distortion and corner resolution-fall-off with FF 35mm, when used as a standard 24mm without shift.
However, I wonder about the usefulness of shift for architectural perspective control when we have perspective control (as well as skew and distort) in Photoshop. It seems that 'shift' is perhaps more useful for seamless stitching of close-by subjects with negligible parallax errors.
Tilt could be useful for extending 'apparent' DoF (if you can get it right, which is not all that easy), but f16 with a 24mm lens can produce very good DoF with little loss of absolute resolution (on the 5D, anyway).
I have the 24/TS-E as well as the 90/TS-E. For some reason, I don't use them as often as I should. It might be because they are fairly heavy lenses. It might be because I'm not keen on fiddling around with twiddly knobs and spending more time on technical matters than compositional matters and losing opportunities of the moment. It might be because they are primes, and I simply find zooms more useful.
When purchasing a lens, you should consider carefully the likely usage, especially if money is an issue. It's easy to become enamoured of the possibilities and potential of a lens, then find in practice it's under-utilized.