Two at the maximum, imo. If you really want to get the A-range, you need to discuss them *in-depth*. No, really. That means analysing extensively the many many themes that exist in each poem that somehow relate to imaginative journeys. You really aren't going to impress the markers if you analyse 3 poems by only stating half a page on each theme, remembering you still have to analyse 1 stimulus piece and 2 related material. In fact, in the 2004 marker's comments, it was pointed out that numerous responces were placed in the A-range by only analysing 1 poem extensively.
Basically if the question asks for at least 1, DO just one (or two if you write fast). If question asks for two, DO just 2. Roll with the question.