>>1562959a better saddle would be my first rec, plus clipless pedals and maybe a new groupset, depending on how well you've taken care of your existing one. i can't make it out from your pic but if that's the 2006 R700 then the 105s are in desperate need of an upgrade. you'll notice a massive increase in shifting quality as well as a drop in weight if you moved up this-gen 105 or last-gen ultegra - if you can find it cheap you might even benefit from DA 7800 which is roughly the same year as your existing one.
carbon wheels are great, but they're really expensive for what they are. you can save money by focusing less on weight for now and more on making a well-fitted, more operational machine. plus newer higher-end components will drop weight anyway, especially the saddle.
