Miss Spot I am inclined to agree with you. Even if a guy sends a really good message and gets a reply it may not mean much because she might not actually be thrilled with him about anything past that 1st message.
I pretty much agree with you too. I think it's not how Good the initial message is -- it's about it not being Bad. A well thought out message to a profile IF/when there's a lot written in said profile, can do something, but as you point out, it soaks up too much time. I would say a "Hi there. :)" is a little "bad" -- although it's not a killer obviously.
I would say a good test would be something Simple and easily repetitive to a variety of profiles, not requiring thought ("Great [smile]. :) Are you originally from the [city] area?") VS 4 full-sentence message noting something specific in her profile to ones in which there's something to feed off of. IMO, a guy should only pause to do that when a gal has a lengthy profile and she Really stands out to him. Otherwise for lengthy profiles -- something in-between which still doesn't carry much thought would be good, where there's something that pops out that you acknowledge or ask about if it yearns a question.