In simple terms, what can I get out of journeying to the End?
The biggest incentive for going there has to be the Enderdragon. Killing it is required for "winning" the game, gives you a ton of XP (the equivalent of 4000 zombies), and drops the Dragon Egg block, which is in itself useless other than as a trophy. Bragging rights, I suppose.
You can also get a material found nowhere else, the End Stone that the place is made out of. It also serves no purpose and isn't particularly pleasant to look at, though.
Other than that, it's crawling with Endermen. You can use this for XP grinders — from holes in the ground from where you hack away at Ender-shins, to huge spawning platforms that automatically drop the Endermen to ½ hearts of health.
Example of such a grinder setup: