Two things - I am late with the first, but one of these "steam caddys" seemed like the answer for the gentleman with the old vivitar - the steam does wonders to remove stubborn dirt. Unless the heat cracked the lens, but I doubt it.
Now, as to the "dirt does nothing, scratches do" question. Yes, a crack or a scratch is structural damage to the substance of the condensor. As such, it acts as its own, totally unpredictable lens/prism. Dirt, stains, etc., do not.

My Omega has a what looks like a water spot on the bottom side of the top lens of the condensor (its two pieces of convex/flat glass, with the convex parts facng each other). I assume years of temperature changes and condensation built up moisture on the glass, and when it condensed, it rolled to the lowest point and eventually dried there. I looked at cleaning it, and decided that a misaligned condesor would be more obtrusive than the little water spot. So far, I have been proven rigth, as I see no artefacts that I could realte to it on any of the prints I have made.
This is by nomeans an argument against cleanliness - I go as far as I prudently can to clean my lenses, etc. Its just about sme trade offs that might be worth making (lesser of two evils type thing).

Well, just some thoughts from a beginner - do take them with that in mind,