While PS Plus will be required for online multiplayer on the PS4, you'll also get access to the Instant Game Collection and the ability to cloud-save your games. The PS4 will also limit your music-listening options to Music Unlimited - which is kind of ironic when you think about it - so if you want to crank some tunes, the trial will get you started.
The $10 voucher is arguably the real treat here, as you can use it however you like in the PlayStation Store. Movies, games, TV shows and more will be available on your new PS4, but if you're a Call of Duty fan, you've probably already noticed that $10 is the same amount it will cost to upgrade from a PS3 copy of Call of Duty: Ghosts to a PS4 copy.
Update: Note that Ghosts isn't the only game that can be upgraded for $10. Battlefield 4 will also be available to upgrade for the same price, as will Assassin's Creed 4: Black Flag and Injustice: Gods Among Us Ultimate Edition.