Hi Blaughn
I will be honest with you, sometimes I walk away and re-wash the neg, sometimes I get someone else to give it a go. (we are talking cibachrome) and yes I am an excellent spotter. I learned in 1973 from Don Dunsmore how to spot while I was at college and I have owned and frequently use a Windsor Newton #2 .
I print a large majority of my work and others with 35mm and medium format negatives. There is a huge difference in sharpness , between using glass or not using glass. Some workers confince themselves that there is not as they do not like the cleaning process and as well have never learned how to spot a print.
If you are using 4x5 primaraly, as I stated earlier I think you should be ok without glass as the film is thicker and more stable, As well I would use JMdavis technique of heating the neg up . It sounds like a very workable method for 4x5.
Now to be really honest, I cannot imagine how a worker would choose a diffusion head over a condensor head, In fact I am buying a point light source
(ooch) to get even more dust into the mix.