I'm relatively new to all-grain (7 batches) but the main points I like about it versus extract is:
1. More options, ALL the different grains to mash, mash temps for malt profile, etc. its a lot to play with, and i am enjoying learning as I try different stuff.
2. I'm a hands on kind of guy, so it was the best way to get more of the true brewing experience, and be more involved in the process.
3. Cost per batch. My all-grain batches are about $15-$20 less per batch, compared to extract versions, the recipe i converted and remade was $20 less.
4. Quality - I really think the all grain beer i have made is overall better than the extract brews i have done.
The cost to switch to All-grain brewing was minimal, and with the savings over extract, the equipment has paid for itself. I spent $80 on a bigger kettle, and $25 to convert a cooler. I havent switched to a tiered setup or anything, i just do a lot of lifting.