Regarding the 1st message topic useful poster - as mentioned at #3 message above - my intention was to incentive the thanked newer member motivated to keep sharing updated informations, but as you said, this feature really have no effective utility, at least to me.
I believe it serves another purpose too, as it can help noobs asking questions to evaluate the replys they get, especially when conflicting answers are given by different members.
For example, someone with posts=1000, helped=300 is likely to be someone who's generally helpful and probably knowledgable, whereas someone with posts=250, helped=2 is likely to be someone who isn't very knowledgable and has more questions than answers themselves.
(Just my 2c worth)
P.S. as for the thread topic, I'm not bothered that 1'st posts can't be rated.