So much for vigilance. Now to relax. Dirt happens, and in moderate amounts it has remarkably little effect on performance. In his book Star Testing Astronomical Telescopes , Harold Richard Suiter analyzes the effects of dirty optics mathematically. That's quite a pile of crud before there's any detectable effect on contrast.
All mirrors fail such a harsh inspection.
After you've done what you can to prevent dust, ignore it. There's a good reason to ignore dirt aside from maintaining peace of mind. A dirty lens or mirror can always be made clean, but a scratched one is scratched forever. So clean optics rarely. Actually, the surface you are cleaning is usually not glass but an optical coating that is softer and more vulnerable.