Grishka said: "If the poem has a fairly regular metric structure (as Alaska Mike's one above) and/or many verses, and a "folkloristic" style is desired, this will limit our creativity."

Overly regular meter is a challenge, particularly since older poetry tends to be relentlessly regular. But I look at the situation differently: it's a springboard for another set of questions that provoke your creativity. Amid the usual prescribed conventions, how does one introduce variety? The vast majority of traditional songs may sound rather drably uniform, but there is still a plethora of songs that are musically interesting despite having regularly metered texts. Examine them; what makes them stand apart, what grabs your interest? What techniques do they use to avoid dull regularity? You don't have as free a hand as with a modern song, but that may help you focus on more subtle techniques for creating interest. And nowadays, a little modern (in)fusion will hardly lift eyebrows.

The only thing that really limits your creativity is the belief that your options are limited.