I was wondering why Charlotte died, when seemingly Dan was a constant for her (she met him in both 1977 and 2004, and at the end she seemed to be CTT).

Well, using this definition from Lospedia:
Daniel Faraday (http://lostpedia.wikia.com/wiki/Daniel_Faraday) explains that when a consciousness travels back and forth through time (http://lostpedia.wikia.com/wiki/Time), it needs a constant to latch on to. A constant is an object or person that exists in both periods of time, that the traveller deeply cares about and could recognize. If a constant is not found, the oscillations between different times will become more frequent and chaotic until the individual dies from what appears to be a severe brain aneurysm (http://en.wikipedia.org/wiki/Cerebral_aneurysm).It seems that, despite Daniel's efforts to get Charlotte to care for him in 2004, Charlotte wouldn't have recognized him or cared about him in 1977.

Maybe Daniel should have stayed on the island in 1974 and gotten to know the little girl - talk about a variable that can change things. Or maybe he should have taken her to the swings in 2004 (or subsequent flashes).

Agree or disagree?

p.s. I have discounted the reason being physical vs. consciousness time travel for other reasons.

I agree. When she was a child Daniel was just a crazy old man who told her never to come back. She remembered him, but I don't think she would have been attached to him at that point.