I also would rather not bother and I really can't believe I need to stretch my upper body EXCEPT maybe triceps if I've done a lot of overhead weights. But having said that I do have a bit of hamstring pain today, having half-arsed those stretches yesterday. Sometimes I get away with it but every so often, not doing a proper stretch seems to have minor consequences.
Stretching is the best bit - most classes rush through it and don't do it properly imo.
Yes it is important.all the time you manage to carry on injury free you think you can get away with it but it will catch up with you and you'll end up either but of you so stiff you cant do the classes at all.
It's not the immediate effects that matter the most but the long term effects of contracting your muscles trough exercise and never counteracting that by stretching - can lead to injuries over the long term.
If you're lifting heavy enough in pump, stretching properly will make a difference to the delayedonset muscle soreness you feel next day too. If you don't feel it you need to increase!
proper stretching so you may be right that there's no real difference whether you do it or not. If you want to continue working out (or walking!) into your later years it us important to do it properly.