Tooth brush (hard) and mild soap, except on the stickers. With the decals and stickers is better to work around them or just cover it with with plastic clay or Silly putty or something like that, just in case the soap damages the colours or the glue of the sticker. In the 3rd picture I see brown spots, but for me they look more like rust that went through the paint. Maybe something to remove the rust will work there, but it might also damage the paint. In my opinion I will leave any dirt alone if it doesn't come easily, but you can always try to use any harder soaps, alcohol or chemicals in a non visible place of the crinkle paint and see how it does react to it. 

Thank you steini