this is how i like to set the differences. PIAA spark blue bulbs will light up blue lights, HID will project light with colors you prefer.
i would say not only spend 100$ extra for the HID, but 200$ extra to get it perfect. spark blue is just nice cz its not as expensive as HID and has a real nice color, plus its legal cz some states HIDs are illegal(CA for instance).
in order to get the best output from ur HID kit, you need to get a good ballast and a nice bulb, plus valeo projectors. this is if you really want ur HID lookin nice and its best and comparable to german cars or other cars that come with HID stock. the reason why you need to put 4300K HID bulb is cz thats the best output you can get, higher you go, you lose brightness and gain color. i wouldnt recommend this even after buying a 6000K HID bulb cz the output will be lower than the stock one you had and you cant really see shit at night on some streets cz the cuttoff lines are strong and uneven cz our projectors arent made for HIDs. thats why you need to get valeo projectors, which are famous projectors used in some nice OEM HID kits that come with the car. the valeo projector not only gives you the cuttoff lines just like other HID equipped cars, but it will project the light at the right place with the right amount. it also gives you that blueish color you want from an HID kit. so the best way to get the blue color you want from an HID kit is to go with 4300K HID bulb with valeo projectors. the projector reflects the blueish color, ur bulbs dont have to project blue, which is why a lot of ppl go with higher K bulbs cz they want the blue in the light. consider this, ANY OEM HID kit is nothing higher than 4300K. even s2000, BMW 7, MBZ S,...
i hope this was helpful.