First off, the main difference between the rep system and the like/dislike system is the fact you can see what posts are liked/disliked where individual reps are hidden. Why is this important? Reputation would show how much a specific member is liked/known within the community, and that system achieves it. However, it is an older system which was also abused heavily so its use has been in decline, but that is also why a person's reputation is more significant now: harder to achieve.
The like/dislike system is different on the other hand because it is designed to show how members like/dislike certain posts or threads publicly. Every site nowadays has a feature similar to this. They are two different systems for achieving two separate results. By not having this system affect the reputation system, it can't really be abused and therefore a person's ability to like or dislike freely (though dislike has apparently been restricted) is protected and it also achieves the 'social' aspect that the admins are looking for. If the like system did affect reputation, its use would be restricted in the same way the current reputation system is limited, and thus would fail to achieve the social look, because members would only be able to like/dislike 1 post of each member until they like/dislike enough of other members posts. For someone like me, I tend to only rep certain posts by a limited group of people, and it may be months or even a year before the same person gets another rep from me.
What that means is, if we combined the two, chances are anyone visiting the site would see few, if any, likes since you wouldn't be able to like/dislike at will.
Are both systems a bit pointless? In a way, but several members including myself, enjoy them both and value how each allows us to express ourselves. It also cuts down on the generic "i agree (but will not add any other input)" posts since simply clicking like or dislike expresses that agreement or disagreement.
-J
