I learned so much about my toons when I played them solo. I realized I had missing gems, enchants, and the wrong glyphs.
Dont try to box cutting edge content right when it comes out. Once it loses the "ooh shiney" effect, and ppl learn the fights and start to outgear it, then you can start to think about boxing in raids, provided everyone else knows their role. Usually having a really good healer or a really good dps, or a really good tank can help round out other deficiencies. In my guild, the healers are friggin awesome. Pugging some raids where the tanks and DPS way outgear it, we wiped due to healers not being as leet as what I'm used to.