Discounts of any sort is good..I would make that on full details....promo on car wash only is good...I would limit the amount of people that you have handing out flyers on a busy street, last thing you want is to distract a driver and have them crash...and the biniki thing is sending the wrong message...there are plenty of ladies that pay for car cleaning and might be offended by that....
If you have a place that you can rent one of those canvas figures...like you see at car lots a giant gorilla or something like that...its a good attention getter....people notice that from a distance and wonder what's going on...a figure on the top of your shop will attract attention!
Give a-ways or raffles are excellent...people love being able to win something...the food is also a good idea..keeps them at your location longer....jumpy jumps for the kids...again you are trying to keep them there longer...spread out the raffle give aways..and use a bull horn to announce it...I know this all sounds funny and circus like but that's what gets people attention and what the media likes to cover!
Give away logo t-shirts or stickers for windows
Car wash club by the month see about getting people to sign up and pre-pay for X amount of car washes.
Have you done a press release to the local newspapers and tv stations???
Its worth the time to see if they will give you a spot or plug.