I don't think you look dowdy. But, I agree with chewy and crw that you could break up the twinset. Both are great pieces on their own, and you will get a lot of mileage out of them. But together, it's a conservative look.
Also I think the twinset is not quite skirt length - it's a tad too long. A belt would solve this and make the proportions better.
You may feel less dowdy in a flat that has a lower vamp, like a ballet flat, or a thong sandal. The sandals are quite adorable and the black is a great choice with your hair color, but the straps interrupt the long lean line, which may be why you feel the skirt is too long. It's not, it's a perfect length.
So... try a ballet flat or thong. Hike the shell up a few inches to get an idea how a shorter length top would work, or belt it. Then toss on a different color cardigan (I bet turquoise would look great). Or wear that cardigan but maybe pair it with a skirt-length graphic tee?
If yummy mummy is what you are going for - covered but sexy - how about trying a wrap shirt? I bet you'd look amazing in a wrap top. Also what about baring your arms? I suspect sleeveless would look great on you - showing off bare arms (while keeping cleavage covered) is sexy but tasteful. Another good style to try is a cowl neck top.
