I absolutely think that we have a moral imperative to go to every measure possible in preventing the extinction of a species. Name me a species that is on a threatened or endangered list that hasn't been put there by our direct action.
I work in conservation and I can't think of one off the top of my head.
The thing is, with animals like pandas, you can treat them as an umbrella species - they need a lot of habitat to meet their needs, so by preserving sufficient habitat for the bigger species, all the smaller species that share that habitat benefit too. Also, as much as I love snakes and spiders, there is just no denying that it's way easier to get support for the conservation of the "charismatic macrofauna" - the big, handsome species like tigers and pandas. The little creepy crawlies are every bit as deserving of conservation efforts, but with the biodiversity crisis we are currently in, I don't know that we have the luxury of time to fight the PR battle for endangered bugs and reptiles, as well as the conservation battle. I teach about it all the time, and I certainly advocate education as a very important tool for conservation, but for effectiveness? I would put my money on the big and glamourous species. Pandas are an international conservation symbol for a reason.