It's not a question if you should or not (obviously!), since music is free, unrestricted will.
As far as i understood, according to your question you might be asking it differently "should i add a counter-melody?" or "is the first melody or counter-melody more effective?"
Most important thing is to consider that the counter melody is a "second voice" in the conversation, which is not just a harmony part to the first melody–It provides harmonic support for the first melody and it differs from simple harmony that it can stand on it's own and work as itself.
Counter melodies in compositions can either contrast or resemble the first melody, sound background (supposedly) to the first melody, respond in a "question-answer" type of manner to the first melody.
Since you thought of playing the melody only, or to play the counter melody with the first melody sought– Another thing to consider important is that counter melodies are written mostly after the compositional "meat n' potatoes" part (harmony and rhythm) and is a result of simultaneous voice leading.
So the two articles i thought to be both effective for your question and interest are both listed here:
Steps to writing an effective counter melody (the article is informing, not the consumerist-page design itself)
How do you write a counter melody?