As for human emotional signals in aliens--I always thought it was a very nice touch by Leonard Nimoy, or whoever was responsible, in "Enterprise Incident," to establish that Vulcans and Rommies don't kiss with their mouths. (Not to suggest that it is a problem in ST11 that they do; he's getting it with a human, who wouldn't get much of a kick out of holding hands).
He also mouth-kissed Leila Kalomi and Zarabeth in TOS. Leila was definitely human, and Zarabeth at elast looked 100% human, although from another planet. So it's nothing new to see Spock engage in mouth-kissing with human women. The only time we saw him with a Vulcan or Romulan ("The Enterprise Incident", TSFS), they were engaginn in finger-touching instead.
However, Trek hasn't been particularly consistent in providing different alien races with different emotional signals. Klingons have their own specific ways of courting and making out, but many of the alien races in Trek seem to engage in the same kind of mouth-kissing that humans so.... Bajorans, Cardassian, Trills...
As for the blood color, I wonder where the idea about Cardies having brown blood comes from. I don't remember it ever mentioned. Garak's blood looked red, and we've seen both Dukat and Damar with bloodshot eyes (not that it would be worth changing this is post-production, anyway
I have been very tempted to comment that you are all overthinking this... I am prefectly OK with the realities of making a TV show that dictate using human actors, for starters
and letting them still look sufficiently human-like even in makeup - I admit that I never liked the more puppet-looking aliens as some of those in "Farscape", which aren't any more realistic, for that matter. If we ever got to meet actual aliens in RL, I'm sure that the differences between them and humans would be far greater than the color of blood. There is no reason why they would look like any species from Earth. Maybe they'd be pieces of goo or something.
Trek has had several worthy attempts to portray trully alien
aliens, but in these cases, they either had to appear for a short time, and to possess a humanoid body to even be able to communicate with the humanoids (Medusans, Prophets), or, in the case of Changelings - Trek's most alien major alien race - they had to keep a human form 99% of the screentime so they could be played by actors, communicate etc., which results in viewers too often practically seeing them as humans and forgetting just how different they are supposed to be.