1) what are the major components needed to jump from extract to AG?
You can brew in a bag and still brew all grain. Or you'll need a mash tun and a kettle possible of doing full boils. The AHA just did a video on all grain brewing.
2) is the learning curve steep?
Depends. Can you do it? It's not hard. Can you do it well? It takes a bit of fine tuning to get everything right.
3) how much longer are brew days?
My extract brew days were 2.5 hrs on average. Now they are 4.5 hrs.
4) is there any noticeable taste difference between AG and extract with similar recipes?
No. If you aren't brewing good beer with extract, don't switch to all-grain. It will likely not help. Or in other terms, riding a motorcycle makes no sense if you can't ride a bicycle with training wheels.
5) if not, what's the point?
More control, more experimentation, more gadgets, etc, etc.