1) Mites can be seen without magnification and are therefore nirah leayin, Anyone who knows how to identify a mite will tell you that it is visible without magnification.
2) Dov, your process will not remove leaf miners (found in almost all types of leafy vegetables). In certain vegetables insects that would normally come off with soap and water after soaking and brushing can hide in cracks such as in broccoli florets, or thrips hiding behind strawberry seeds. If you are trained to identify the insects that are commonly found in vegetables (i.e thrips, aphids, mites, leaf miners) and how each one can be removed, then you can check your produce yourself and clean accordingly, but for those inexperienced in identifying bugs I would suggest using a cleaning method that has been tested and is recommended by an expert. Rav Vaya’s “Bedikas Hamazon” sefer, and Rav Revachs “Tolaat Shani” sefer are excellent seforim with clear instructions and pictures on how to clean different types of veggies.