Valium I know exactly what you mean. I've refused tests as I told them it would make no difference to me, and as you, my age would give me a high probability anyway. Also like you I've now read a lot of the threads about the poor families who have found chromosomal abnormalities and have looked them up so it does give you something to think about.
On the bright side my mum was 42 when she had my (older) younger sister and 44 when she had my youngest sister, the only problems were due to her being rhesus negative and both needing a blood transfusion, but obviously that was absolutely nothing to do with her age.
My hubby thinks I'm being melodramatic when I told him just yesterday that I'm not getting anything until after the 20 week scan, he wanted to buy the pram yesterday and he is more excited about this little baba than when I was pregnant with the other 3 :) He says I'm being miserable.
It's a worrying time for us mums, but we'll soon be glowing and very large :)