Should I approach sponsors I already have a discount relationship with?

Remove stickers from brands that aren't providing substantial sponsorship value. If a wheel company gave you 10% off and you're running their sticker, potential sponsors assume you have a real relationship with that company and may not approach you. When Andy McMillan returned to racing, he removed all non-paying sponsor stickers and showed up with a black truck - then won the race. This demonstrated he was open to opportunity. You need to clearly signal you're looking for real sponsorship relationships, not just discount deals. Getting paid to race is cooler than having a lot of stickers.