Plants really don't help or hurt a cycle. Plants consume nitrogen for their growth so they can make your numbers a bit harder to interpret. If you have plants in a cycling tank just let people know so they won't be misled by your readings. The ammonia you add will be shared between what the plants can use and what the bacteria can convert. What happens will be a drop in ammonia without a rise in nitrites and that will confuse people if you don't tell them about the plants. It is really no big deal one way or the other as long as all the information is presented when you ask a question.
I did a 30% water change two days ago, but I would still expect the nitrates to be accumulating with all the nitrite being processed. What gives? I won't be able to add any fish until next weekend, so there's still time for things to happen.