1) what are the major components needed to jump from extract to AG?
What others have said. You may want to try Brew in a Bag (BIAB) if putting together a mash tun/manifold is intimidating, or if you simply want to keep things simple.
2) is the learning curve steep?
There is a lot more to know with All-grain, but you don't *have* a lot to get started. Steep some grain in your mash tun for an hour, run it out.
3) how much longer are brew days?
I don't recall how long extract days were, but AG can be a little longer, 4 to 6 hours depending on your sparge setup and what kind of mash you're doing. Again, BIAB brewers may have a brew day more similar in length to extract brew days.
4) is there any noticeable taste difference between AG and extract with similar recipes?
Extract beers can be every bit as tasty as AG for certain styles if you have very fresh extract, but for other styles it's harder for Extract to match AG in my opinion (see next point).
5) if not, what's the point?
All grain really gives you the freedom to get more creative, as well as craft more authentic-tasting beers for certain styles that it's hard to make with extract (i.e. Witbier). It's hard to get the flavor of Wit just right using Wheat extracts, not to mention the milky pale color. For me, the gear/geek-out aspect isn't so important, but then again I'm just not a gear-head. I like to keep my setup simple rather than complicate it with gear I don't need. I'm strongly considering trying BIAB even though I've been using a more traditional AG setup for a few years now.