The covers you pointed too wouldnt be able to withstand the forces put on them by small road debris, would most likely crack and destroy the headlamp's reflector (and make the bulb explode if it was one) when moisture got inside.
IMHO, covers in general are pointless. Even if the car had true HID (D2S type bulbs, not halogen bulbs) you would still be near stock output because of the light loss of the covers.
Polish everything back up, if you want darker headlamps do the Hightower mod while you are working on them. Silverstars are a inexpensive lighting mod, when considering other lighting mods, and they produce desireable results. True HID however, like Irda said, costs considerably more.