Yes, you can use Psynergy with just the buttons if you want, and it has very nice targeting. Psynergy will auto-aim to valid targets (and, if there is nothing in range that can be affected, will cancel without spending your PP), and you can cycle through them with L and R. Then you can use the D-Pad to choose direction (for something like move) or just A to confirm for things like Growth or Cold Snap (the new Frost Psynergy).

Most Psynergies now have much more functionality. Growth is a default Psynergy for Matthew, and is used throughout the game fairly regularly, and plant ladders are very common (and, once you make them, they are permanent, a welcome change). Arid Heat (what was once Piers's vastly underused Parch Psynergy) is used in many more places, and has combat uses as well (as well as higher level versions once you equip the gem). Whirlwind has more uses and is used more often. They just really expanded some of the limited functionality Psynergies, and it works great.