Skimmed through the thread so apologies if I'm repeating what others have said. My thoughts:
Colours:
You are promoting a company which cleans cars. The brown colour to me really doesn't conjute up thoughts of cleanliness. Brown really conjures up thoughts of mud, dirt, grim etc. Which whilst yes the cleaning will of course deal with these, you really want to be putting clean thoughts into peoples minds with the colours.
Either nice bright fresh colours, or white with hints of nice fresh colours - think blues etc. COlours that willbring up mental images of water suds etc.
Photos:
The Audi covered in foam is a great pic. The Corse, while looking nice and shiny, it is not exactly an inspiring car or image. if you have any other sparkling clean car pics I'd use something else.
Background colour:
Nice as the idea is of using a tint for a background, I saw you mentioned that you'd be folding the flyers. Solid colour does not go well with folding, it'll leave at best obvious creasing, at worst cracks in the colour which will look terrible.
Following on from my comments re the colours, a nice simple white background will not only feel cleaner, it'll also get rid of any back ground cracking problems...
Size:
Personally I wouldn't go for A4 for a flyer of this type. There is not a huge amount of info on there so you really don't need that much space for it all. I'd consider moving down to A5 as you will easily be able to fit everything on the flyer at easy to read sizes and you'll get 2 flyers per sheet, so either double the number of flyers or half the printing needed...
Logo:
I like the W part of the logo with the water droplet but the rest needs a bit of work. Even simply Having the "Will & Joe's" on one line followed by the "Mobile Car wash" then on a third line "& Valeting Service" would work better I think.
Text:
Fonts could be better.
Also, I think it would be good to be a bit more clear about the pricing structure.
For example: Valet from £30. You say Full Wash and Vac plus Hand polished and waxed....etc etc
Do I get all that for my £30 or are some of those extras on top of the £30? Does the price increase with more treatments or is it based on the size of the vehicle? There is nothing to tell me this, which could put people off...