If I had to decide between just +1 and +1/-1 rep, I'd also simply go for +1.
I just wasn't sure if there was a -x possible currently (since that star first reminded me of a bad cop sherriff star ).
About "what are rep for" - well, I thought it can mean anything. To me a well done map is worth rep just as much as a helpful tutorial on techniques for example. For "this is a great map artist", we do have the awards, don't we? (although of course it doesn't mean that members without awards yet are not )