Hey MarshalN,
I know you're much more familiar with Chinese teas than those from India. To gauge differences between high quality Darjeelings, I'd recommend to try a few teas side-by-side as the acid test.
As with most flavors we're not too familiar with, people tend to notice the general characteristics of a tea (type and growing region) when tasting a single tea rather than its own (more subtle) character. If you do direct comparisons, you'll start noticing a lot of subtle nuances that make each tea quite unique.
Do all high grade Darjeelings from a particular flush look (and pretty much taste) the same? Hardly (just have a look at the leaves of Arya Ruby, which are about 2-3 time the size of the leaves pictured and much darker), but in general terms, they do resemble each other. But to people not familiar with Chinese tea, most Wuyi Yan Chas would also look almost identical. But we all know that not only are there at least a handful of different types, but also a vast number of different grades.
I did some experimentation with brewing Darjeelings in a small pot. Sometimes, it works wonders and each infusion reveals new insights into the tea. Sometimes, the tea turns out just plain boring. Especially with second flush Darjeelings, I found that "British style"-brewing (big pot, decent amount of water) often produces much better results than a small pot. But then, some first flushes were just amazing when brewed gong fu (I particularly remember a fist flush from Puttabong Estate which seemed to produce new flavours with each infusion).

Entirely true, yes

However... I tend to think of myself, with regards to Darjeeling, as an average drinker who knows little about Darjeelings specifically, but know something about tea generally. I'm sure if I immerse myself seriously into this, I can probably find lots of interesting things (and I should say that even with my drinking these samples I can tell they're not the same -- just not THAT different). What I mean to say is that for the average consumer out there -- how obvious would these differences be?

I get your point (and I had no doubt that you would find differences in the teas).
How obvious are the differences for the average consumer? Good question and one I had asked myself numerous times until I tested it. I held a tea tasting with about 25 people - almost all of them completely inexperienced tea drinkers - with 7 Darjeeling teas (3 first flush, 3 second flush and 1 white). Deviating from my usual practice of serving one tea at a time, I served 3 teas side-by-side (for the FF and SF) and then the white tea by itself. I was just curious if people could taste the difference (I do, but then that might be due to excessive exposure) and how the teas would compare. The result was very interesting, because everyone thought these teas were all quite different. Everyone had their favorite, only one tea was completely off everybody's list (I cheekily served a supermarket-bought Darjeeling in with the SF teas and people just wouldn't touch it after the first sip). The tendency was clearly in line with higher quality scoring better with most people, but some people just liked a stronger tea better and favored a lower grade tea.
This answered the question for me, but you can try it out for yourself by serving your samples to average tea drinkers side-by-side. I'd be curious about the results...

MarshalN, I highly appreciate you sharing your tea experiences with the online world (sometimes I can't understand how you make the time to drink and describe all these teas) and with your background, I am sure you don't have to immerse yourself too seriously into Darjeeling to appreciate the differences. Just do some comparative tastings, you might be surprised.
But saying that, I realize that pu-erh and oolongs do offer an incredible range of experiences and we usually don't have enough time (or interest) to invest equal amount of energy in all types of tea.