Well for the shaders, not really very important your 3D art is already very great like that and lightmaps !

For Depth Of Field , necessary only if you have distant 3D models
like moutains, or for cinematic. If you use a good skybox with blurred mountains, it will work as well and you'll keep good framerate. Perhaps DOF will do a great job ?

You are right, good effects makes games visually appealing especially when they are exagerated, it gives lot more life to the scene and more power felling to player when it's attack effect like in games like Ratchet and Clank or Zelda Wind Walker !
Zelda Wind Walker

I think the more you work on this game , the more you'll be skilled in this style of game indeed and in level design !
Perhaps you'll make your own Metroid like game after that !