Thanks for the replies, I'll check out Building Panos after work.
The extra reach would be nice for traveling. I hate taking extra lenses and wish I could have a one trick pony. Though I've heard (and noticed myself) that the 24mm end of the 24-105 isn't great. I like my building and landscape shots so that might dissapoint me. My 17-55 gets used at 17mm a lot.
I don't do macro but sometimes I like to take close up type shots. Things like rings at weddings or flowers, that sorta thing. I usually just crop the image to make it look like a close up. Maybe the 24-70 f/4 would get me into macro? Who knows.
Yeah I think I'll wait for the price to drop. It's tempting to get a 2nd hand 24-105L. Currently the 24-105 is going for about $750 2nd hand (¥75,000) but $950 new (¥96,000). The 24-70 f4 is going for ¥127,000 (I live in Japan hence the yen).
I recently sold off my 85 1.8 and 50 1.8 II so have about $400 or so extra. Was going to buy a Sigma 35 but might do this upgrade first. Decisions decisions.