Thanks again to everyone who is contributing.
To the one person who's dissing the crux of the thread; I don't see how what I'm asking is invalid. One possible function of a digital camera is to use it as a light meter. You cannot dispute this fact. I do not have to depress the shutter button on my 5D; I do not have to take a single digital image. I can still use it "as a light meter" (in this regard, it's no different than, say, a light meter app for a smartphone).
Some of the very strong arguments I'm seeing here is incident metering. Taking a look at a page like this (
http://www.sekonic.com/Classroom/MeteringTechniques/IncidentvsReflected.aspx) has given me a good idea why that is very useful in some scenes. I'd need to learn more about it to get a full grasp on things, but, I guess if that is what persuades me, then the Minolta sounds like the way to go?
Flash is not something that I see myself ever getting into, so while flash metering seems to be another strong area in favor of dedicated meters, for me, it's not so pertinent.
Matt above me I think raised a really good point that I hadn't thought about, which is consistency. Very true, at any given time, I may have a different lens on my 5D (17-40L, TS-E 17, C/Y Distagon 35/1.4, Helios 40-2, etc being some of my favorites). I can see how that could be problematic RE: getting consistent and reliable readings.
I do wonder, though, if much of that could be ameliorated if/when something like the Light Meter app on my iPhone becomes more reliable (I would love to ask people here who use it, along with your other dedicated meters, about the reliability of those things).
Please understand that I'm a variety, if not necessarily of the generation (I will be turning 40 next month), who grew up never needing a light meter, as I've always shot P&S & newer SLRs, and when I got serious about photography and film specifically, just three years ago, I already had these digital tools that not only I'm accustomed to but are really the ONLY tools that I've ever used for metering purposes.
I'm a bit torn about the Pentax, as someone said that's the only "true" spot meter, and I see there are a couple vocal advocates.
Regarding spot metering, one thing I love about the iPhone app is that it allows me to tap on the screen to choose where I want it to meter. I'm assuming this is very close to what spot meters do, albeit perhaps not at that level of precision. Another thing I love about the app (and using digital cameras in general as meter replacements) is that I get a visual feedback of exactly what the scene would look like if shot using the readouts they give me. That's one thing a dedicated meter can't do.
So, my question here to those skilled in the art (and have used them all), are the advantages of higher accuracy and precision so great as to completely nullify the advantage that a digital solution has in that it can rapidly provide a "preview" of the scene for you? I'm sure the answer would be "In certain cases, yes", but then when would they be, if not already stated above? (e.g., flash metering).
My inclination at this point is leaning towards keeping the Minolta and selling the other two, hoping that between the spot attachment, my iPhone, and my two digital cameras, the desire to "spot" can be mostly satiated.
Thanks again for your insights!