5sfe 2.2 Is weak, but solid as a rock!! A lot of people may tell you to swap the engine for a turbo, But a 5sfe is great if you know how to drive it. I seen guy's with 5sfe beating some turbo guy's just with a few mods.
A few things that you can do to your car for more power are Intake - ecu-cams exhaust system and bigger spark plugs.
That's pretty much what you can do to the 5sfe without adding a turbo.
All depends of how much power do you really want and for what use.