This is the first time I noticed your location. You're only about 40 minutes from where I work. Small world.
Cool. I'm in the Woburn area on a regular basis.
What I have noticed about Methylene Blue is that different strains take different amounts of dye to stain well. EC-1118 works well with equal parts 0.1% solution and diluted cells, while WLP566 stains fine with only one tenth of that concentration at 0.01%. If there is significant protein material it may take a little more stain as well. Normally I start with a 2:1 dilution of cells by 0.03% MB and if the dead cells are just a little bit blue I'll measure what is left in the test tube and add that much of 0.1% MB. This gives me a 4:1 dilution of about 0.06% MB. If you have too much MB the slide will look dark under the scope.
I have not played around with determining the reliability of MB staining or improving its accuracy. I'm citing from the literature sources and this is one of the charts I have come across in a German presentation from the Weihenstephan brewing school: