You touched on an interesting question though: When looking back at these series 20+ years later, If Tuvok as a Vulcan wasn't that "interesting", how can any of the other character like Crusher, Troi, Kes, Paris, Dax, etc, etc, etc REALLY be considered "interesting"? Think of it this way: How many personal "Geordi LaForge" episodes or arcs can you have? By personal I mean an episode or arc that centesr on that character, and can't just be re-written for another. Not very many, if any at all. But there were many stories and arcs centered on Worf, Seven, Data, etc.
Been thinking about this a bit and at this point I can only offer a very incomplete reaction.
I think what makes a character 'interesting' to me is how much I can identify with a character or his/her issues. So, for example, Picard is interesting to me because I know the voice insisting on taking the ethical course of action from inside my own head (not claiming I always take heed to it, sadly). Worf is somewhat 'interesting' to me because I can, on some microscopic scale, identify with his struggle of having to live in a society with different norms than the one he got from his cultural heritage. Data is interesting to me because he reminds me of my childhood days when sometimes my intellectual capacity outstripped my capacity to understand things emotionally. Troi on the other hand is not that interesting to me because I don't have a 'supernatural' gift nobody else has, and they made that her defining characteristic. Neither are Geordi (I don't know what it is to be blind), or Riker (I'm not as career minded as he is and neither do I have that daredevil streak) that interesting to
me (they might be to other viewers).
I suppose when we are talking about larger groups of audiences and the writers, they tend to go for the greater common divisor, and also , one character might be "easier" to write interesting stories for than the other. How come we got several stories about Worf and his "warrior" cultural background and how he had to cope with living in the Federation, but virtually none about how Geordi had to cope with being blind (or at least seeing differently than the people around them) beyond a few short remarks? Leaving initial actor ability out of the equation, could it be that it also is a feedback cycle? 1. It is initially perhaps
easier to create a well-written character driven story for Worf than for Geordi (enough people come from other cultures, but writing stories around a 'handicap' is potentially very sensitive topic so perhaps avoided), so
more stories get created over the years for Worf than for Geordi. 2 Because more get created the character gets fleshed out more, making him/her more "interesting", resulting in turn in 3. Because the character gets fleshed out more, there's more source material to base new stories on in turn?
Loose remark: I though Paris was a somewhat interesting character, too. Missing the boat and parental expectations early in life he's shown getting a second chance and taking it, gradually changing his personality from 'con man' to loyal husband and dependable team mate over the years, even if he always kept a bit of flair in 'showing off'. I've seen that happen around me, and parts of it I recognise in myself, too.
Sorry for my thoughts perhaps not being more interconnected and coherent than they are, but I'm still thinking about this...