WiFi works great for me at home and work since I control those networks. But finding & connecting to public hotspots is often a pain and my effort's frequently rewarded with a slow, unstable connection (even for paid ones). In my area, LTE isn't marginally faster, it's way faster than 3G. For me, it's absolutely worth the extra money.
I really don't think having fast, hassle-free internet access on the go is an edge case. Isn't that one of the main reasons people buy smartphones?
For the most part, when I'm out, I'm getting around 6Mbps. The difference between 6Mbps and my friend's (on LTE) 14Mbps isn't exactly staggering when you're reading HN or downloading a photo here and there, and even streaming audio or watching youtube. Mobile sites are already very stripped-down in terms of data usage. If I were, on a daily basis, uploading 100MB videos or whatnot it might make a difference, but for my purposes HSPA+ is plenty.
I really don't think having fast, hassle-free internet access on the go is an edge case. Isn't that one of the main reasons people buy smartphones?