I do, often! I always get most excited for toddler birthdays because I get to find out whose hair/eyes/skin the kid has, and teen birthdays because it reveals more about which facial features they inherited.
I also have difficulty with sims who look the same, partly because I find that Sims 3 genetics are such that it can be difficult to create good-looking male genetics that also look good if inherited by a female child, and vice-versa. So I feel limited when I'm making sims by trying to make ones with genetically "safe" faces.
In the context of a legacy, it can be difficult because I don't want all my heirs to look the same, but obviously they are all related, so I try to introduce genetic diversity through the spouses with facial features and hair/eye/skin colour. As a result, I often find myself hoping that the children favour their non-heir parent so the next heir isn't just a clone of the previous one. Sometimes it works out, often it doesn't lol - my current heir doesn't look a lot like either of his parents, but actually inherited his hair and eyes from his great-grandmother, the legacy founder! Meanwhile his sister looks exactly like their dad, and his brother looks exactly like their mum.