There is merit, yes, however if you are considering it you should think of it as a lever within this deal. i.e. you give that track away in order to gain better terms for subsequent songs all within the same deal. I wouldn't give away the track unless they do that. The worry is that they simply take that single track say thanks and then do the same with the next artist. There are lots of variables you can play with here including royalty percentage, moral rights, how long they retain those rights, what regions those rights apply to, how many songs they/you are tied together for, what they as publishers are expected to do in return and more.
The fact is that this is a situation where the publisher is trying to take advantage of your desire to be published, and your ability to create many such songs. By accepting such a deal yes it can open doors but it also sets out their stall regarding their entire relationship with you. ie don't wait until the deal is done to negotiate what happens with further tracks.
just my two cents