The knock sensors (2) are located under the intake manifold. I wouldn't pull the intake manifold just to check them, but if you have access to a smoke machine, or have a buddy who smokes, fill up the intake with smoke (Pull the brake booster hose or similar, block the throttle body so all the smoke doesn't leave through the air filter) and make sure it doesn't leak by the base. Extremely common, although your lower miles may help.
If you intakes aren't leaking, don't pull your intake just to check the knock sensors/seals. The engine light will come on if the the harness to them brakes or if the corrode and stop functioning.
Plugs are a mileage replacement more than an age, so you could replace them but I doubt that's the issue. Cheap and easy though, so also a "why not".
Wires are more of a time/abuse/mileage replacement. I really doubt they are causing an issue, usually it's all or nothing with plug wires. They will either misfire or be fine....generally. That being said, they are easy to replace, although not incredibly cheap for a quality set (don't cheap out here, big no no).
I don't believe an '05 will have a fuel filter, but replace it if it does. If you can borrow a fuel pressure gauge, or have one, definitely go for a drive with it taped to your windshield. Find a big hill and go wide open throttle up it. It should maintain it's specified PSI, roughly 50-60 depending on your system (look up the specific, don't go by my generality). If your 8th VIN digit is a Z, you have a flex fuel system and can use E85. If it's a T, you don't have that. I believe both systems take different pressures, but it's off the top of my head so don't rely on that.
The exhaust manifolds bolts pop the heads off, alot. So often that Dorman makes a clamp to do repair it easily, although not cheap. We try to drill out the broken bolts, or weld onto them and turn them out when possible.
Usually power loss is due to inaccurate fuel trims, whether your MAF/MAP (usually MAF) is reading incorrect air coming in, a vacuum leak (usually intake manifold gaskets on those) letting unmeasured air come in, or an exhaust leak that is letting oxygen into the exhaust causing your engine to think it's lean (it will try to add fuel to compensate, messing with mileage and power). Without a good scan tool that shows long term fuel trims, it's a crapshoot.
The knock sensors will cause you to lose power, although they will trip the engine light when they are that bad. Without knock sensors, your engine doesn't know if it's pinging and will just retard your timing "in case" you get bad fuel.
Of course, there are tons and tons of other things that are possible, plugged cats and the like, but the intake leak, fuel pump, exhaust bolts, and knock sensors are definitely the most common.
So yeah... take that for what it cost you.
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