First off, is your source an actual DVD player or a BLU-RAY player? Believe it or not, DVD are not HD, the video is encoded at 720x480 pixels, in a progressive scan format. Newer players offer an up-scaler to improve picture, massaging those pixels to fill a bigger 1280x720 or 1920x1080 screen but your TV has the same feature. That RCA cable is carrying all the video signal there is.
Sound is a different matter, DVD's do have "HD" sound, look for an orange RCA jack on the DVD and the TV, use the red or white end of the rca cable to connect those and your sound quality will improve.
Now, HDMI is a good idea, maybe you'll get a blu-ray player down the road. If you cut the ends off the RCA cable, maybe you can use it to pull the HDMI cable, or at least a string, and then the string can pull the cable. Tie the string into a loop so it pulls itself through again for the future.
Wireless HDMI 'should' work with a DVD player, but you might run into trouble with blu-ray. DVD's are going to be firing at a very low bandwidth (no hd video), so the wireless should handle it. However, you get a blu-ray and try to watch something like Avatar that needs gigabits per second of bandwidth for the video channel, your wireless link is going to barf trying to push all that data.
Reading the review, that unit claims to support blu-ray 3d, which is amazing since that's multiple gigabits per second of data, which means there's some sort of trickery going on, since gigabit wireless is still in the lab, let alone multiple gigabits.