I'm thinking of something that would allow you to put an instance at the beginning of an effects chain and one at the end, but it would relate them somehow and show you one simple meter displaying the gain reduction.
 
I'm trying the Brauerize mixing technique, and this would be super helpful.

You could use a stand-alone analyzer such as SPAN (free) or something like iZotope's Insight (not free). Basically anything that it "analysis only" should be suitable.

Thanks for the input. I don't believe that will do what I need, which is show a simple meter displaying gain reduction caused by one or more plugins. I want to mix into a bus and be able to see how much the comp(s) on that buss are reducing the signal... Maybe I'm missing something with these?

Oh, you want a plugin to tap multiple audio points and display the difference. I am not sure of any for that offhand (especially in a chain), but there definitely could be some. You can sit analysis tools side by side, but need to manually notice the difference.

I've used MMultiAnalyzer that way, mainly to evaluate compressors. You insert two instances but only need to look at one of them, as any instance can superimpose up to 16 sources, color-coded to distinguish one from another. Very easy to use - just drop them in and each instance is automatically aware of every other instance. Works better than a simple meter because you can view (and freeze) a scrolling history showing amplitude relationships over time. 

Yeah, it is not a simple GR meter but offers a couple of ways to view differences. Here I have opened up both instances to look at two different views in the Loudness & Wave tab.

scook and bit - this is closer to what I'm looking for! My goal is to push into compressors and keep the GR no more than about -1.5db, so I really need a meter; I don't think I could use MMAnalyzer (which I do have) to easily discern this.
 
thanks!

Sure you can. Give it a try. Gain reduction is just the difference between the two traces. In Steve's screenshot he's got the scale set to LUFS; you'd probably prefer decibels. I'd also suggest suppressing the waveform display to make the graph cleaner.
 
If you really want to use a meter, I'd suggest getting a compact bar-type meter so you can position one directly under another. I had a compact bar-type VU meter on my old computer, but I can't remember where I got it. But there are a number of free VU meters out there. The Sleepy Time DSP one is very nice, but not very compact. The LSR Audio meter looks great and has a peak indicator. 

Hornet's VU-meter is on sale for another 11 hours. Half off at $3.
Edith: https://www.hornetplugins.com/plugins/

That'd be a good one. For 3 bucks, it's not only an easy-to-read meter it's also got the auto-gain and group-gain features as a bonus.