TS-E on the cheap? For architectural photography

I would go for the 6D and 24mm TS-E. Full frame and wide glass go very well together. You get other pluses like better high ISO performance.

Thank you for replying - I'd love to hear more about the advantages of FF, which I haven't ruled out. The ISO I'm not very bothered by, as I'm fine with a tripod and more interested in buildings than things which move. I haven't had problems with my 400D, which I keep on 100ISO almost always.

Another option would be to research used bodies that have adequate live view implementation (factor in screen size and resolution) that you could use in the meantime. If you find a few models that work that are readily available in your area at an acceptable price, you could go for the 17mm TS-E now and buy a slight body upgrade later.

The 650D is pretty cheap online and people tend to praise its Live View, so effectively it would be my cheap temporary upgrade.

Otherwise, I recommend that you continue to save your money by sticking with post processing. You do state that you typically stay with smaller prints. CS6's capabilities are very decent in smaller prints of building exteriors.

The problem here is that I'm thoroughly out of love with the business of shooting wedge-shaped buildings and monkeying around in PS to straighten them up. It works, but I pine for something more like the days of Velvia where you had to get it right with the lens alone. It's certainly worth money to me to have kit I love once again, and where I'm challenged intensely by using it technically well.

I found using a the tilt/shift capabilities effectively can take a lot of time to master. I would definitely want to do such things on a sturdy tripod with live view, rather than trying to squint through a really small view finder.

Agreed! I've given up on the idea of using my 400D for a TS.

Thank you.