Whether you decide to stretch or not, the decision is personal. Some people in forums do not see the merit of stretching.
A very good explanation of stretching, the reasons for it, and the exercises that apply to cyclists is found in the Yoga for Cyclists series at http://road.cc/cycling-health-and-fitness
" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;. Earlier episodes of the series can be found by searching the site. The series is structured so that particular areas can be targeted.
The argument in this series is that as cyclists our movements on the bike are such that we don't use a full range of motion; consequently, over time we are likely to incur some deficiency or muscular imbalance.
It's one thing to be flexible (ho rah) - it's another to be able to put power to the pedals in a lowered aero position...to engage muscles that are adapted to powering in that posture. Stretching is great for some things but you've got to work with intensity in the intended lowered posture to build not only the ability to go low but more importantly the ability to power the pedals in that posture.