The very first thing I'm usually interested in when a new topic challenge arrives (and thus the previous one has ended) is the results of the previous challenge. However while the new one is easy to get to (it's a featured question, after all), getting to the previous is more effort (the best way seems to be to go through the "What should be the subjects …" post, locate the link to the previous challenge, and follow it; not really hard, but still some effort that might be saved).
I think it would be worthwhile to have a link to the previous challenge in the new challenge, so the results are just one further clicks away. Note that I'm not speaking about a list of links to all earlier challenges (as had been in the earliest challenges); one rarely wants to visit earlier challenge than the just-completed one and the list would grow on each challenge, therefore that clearly would be a bad idea (which is probably why that practice was abandoned). However a link to just the previous challenge would not take much space, and would IMHO be quite useful.