Hi, I got the TS-E 24L II a few months ago and really love this lens. The TS-E 17 is very similar and the wider angle of view would be amazing. But for proper landscapes I need filters and this is easier done with the TS-E 24L II. To use at least the lee filter holder on the TS-E 17mm you would have to adapt the lens cap by yourself because this lens has no filter threat.
Panorama shots are very easily done with the TS-E 17mm with the shift. Oft course the main application for the shift feature is architecture and it makes really a lot of fun with such a lens.
The tilt is quite useful to get an extended depth of field in landscape shots. The miniature effect is as big as with longer focal lengths.
BTW, do not get the Hcam lens adapter. It's too expensive and less useful than this one: http://www.photoscala.de/Artikel/Neue-Adapter-von-Zoerk (you can buy it directly from Zoerk if you drop Mr. Zörkendorf an email (see his website). He will quote 220€ for it and it's available in the EU & USA). I got it myself and use it 90% of the time. This tripod collar is really useful to avoid parallax errors and because the larger hole in its base is directly located in the nodal point of the TS-E 17mm and TS-E 24L II. I put it onto a panorama plate and so I can use the shift and take panoramas. This not possible with any other lens + tripod collar combination with a Canon DSLR. Such a shifted panroma is useful for architecture and also for lanscapes.
Where Can I buy that tripod-collar? And the one that fits the 24, maybe it doesn't fit the larger 17?