I'd be very interested in any replies to this question, also. Note Bruce's recommendations from Microlichens of the PNW, v1: Key to the Genera, p1:
Nikon, Olympus, Wild or Zeiss, pass on the oil immersion lens; 4x, 10x, 20x and 40x objectives with 10x eyepieces; good bright-field optics; add polarizing filters for head and light source, and a micrometer reticle for one eye piece.
A side note: I received my copies of v1 & v2 last week and they are a fantastic new resource for Northwest Lichenologists, opening up the world of microlichens, particularly crustose, but their gelatinous, blackish, nonfilamentous and calicioid brethren, as well. The two volume discount deal is particularly enticing. But to dig in, you do need a good compound microscope.