Spot meters with a 5 degree angle of view are a little too broad for a lot of practical work, with overlap and imprecision the limitations. The precise, 1 degree spot/multispot meters are a definite tour de force, as well as the right tool for the job (especially portraiture where there is often overlapping tones and light). By way of mention, incident metering is an equally good tool for uncomplicated portraiture, while landscape use is commonly the preserve of spot meters. There are a couple of Gossens with selectable 1/5 degree spot angles, though you won't nail one for $100 -- more likely $1,000+, also Sekonics (even more disgustingly costly) and a heads-up for the perpetually evergreen Pentax spot meters that pop up on FleaBay every now and then.
Cher Poisson,
Thanks for your observations. I am financially constrained respecting this acquisition and unable to consider $100 or more for a Pentax "find" at present. Before switching to the Luna-Star as my strobe-driven studio and location architectural interior work grew, I used a Luna-Pro, occasionally with the 7/15-degree attachment. I expect the optics in this attachment to be similar to the 7/15 (though I have read that the 5 is superior), making testing and care necessary to avoid "bleed" in reading areas, as you noted. As for the reading circle for portraiture, I think the 5 degrees will not be too wide when my subject is so accessible.
As for using incident for portraits, yes, it's possible, of course, and I did so for years in much of my studio strobe work (as well as in balancing strobe and ambient on location, which the Luna-Star does nicely with it's dual readout. For Zone work, however, especially "complicated" subjects, when the frame includes, for instance, direct sunlight forming a design element on a nearby high-value surface while the subject, possibly in clothing of low value, is indirectly illuminated, direct readings and tailoring of placement and development may be substantially aided by reflected readings.
For a number of years, I did somewhat formulaic portraiture, with well-controlled light ratios and so forth. I am looking forward to clearing that from my mindset and returning to the challenges I enjoyed in 35mm before that chapter began. I hope to get my N pluses and minuses worked out for 35, 645, and 4x5 so that I can be freely open to more possibilities.
Again, thanks for your thoughtful response.