I wear a poppy every year for a week or two leading up to the 11th. I don't wear it to impress anyone, and I don't look down on those who don't.
For me, the poppy represents the sacrifices of the 1st and 2nd world war veterans. I don't very much link it to vets of Vietnam, Korea, Iraq, Afghanistan, or any other recent war, though technically I understand that we are honouring all vets, not picking and choosing.
One of my great grandfathers died at the battle of the Somme in WWI.
My grandfather fought in WWII, and the experience shaped his entire life. He went over as a teenager to fight in Italy, was wounded by shrapnel, and almost died of malaria in a field hospital. Later he helped liberate a concentration camp and fought in Algeria. For the rest of his life he was reclusive and odd because of the experience, and talked about the war until the day he died (four years ago in his mid-80s) as if the events had happened only last week.
My other grandfather fought as well, but I know little about it except that the experienced scarred him so much that he died a severe alcoholic in the 1950s.
Both my grandmother's made huge sacrifices as well: in fact, everybody did. Even in North America almost every factory was devoted to the war effort, and civilians went without basics like oil, gasoline, sugar, coffee, nylon, rubber, wood, metal, and even pencil erasers for months and years because it was needed to be sent to the men fighting. Today we ship off a few thousand professional soldiers to war and then hardly give it a second thought. Suggest to someone that perhaps driving around in a huge SUV is rather selfish while their countrymen die in a war that is (at least partly) about defending oil supplies and they will likely tell you to fuck off before going to Walmart and buy themselves a second or third big screen TV. We have little comprehension of the sacrifices previous generations made.
To me it's these sacrifices of that entire generation that are worth honouring, and regardless of your views on war, it's difficult to argue that WW2 in particular was in any way optional, or that we would have been better off not joining and winning it.
Most of all, I think it means a lot to the surviving members of that generation to see younger people in particular wearing poppies. In 10 or so years, when they are all gone, I may stop wearing one, but not until that day.
