For the parts I mentioned the Mitsubishi OEM parts are very high quality.
For the upgrades you mentioned, OME is certainly decent quality although for shocks, I prefer KYB Gas Adjusts. They're cheaper than OME and work just as well.
For a coil spring upgrade, I also prefer the Gen II coil springs because they're progressive rate springs which ride far better than constant rate springs while also and providing an extra 1-2" of lift on a Gen I. They're also inexpensive at a parts yard.