Yes bodykits are chavvy period. I do exclude the RS body kits etc though, also putting the RS kit on a lesser car just woulden't look right either really as everyone would know thats it's not an RS
Personally I would leave it as it is, plus remember you also would have to declare any modifications to your insurer, thus this will increase what will already be a large premium.
What you would need, ideally, is a repair section for the wheel arch. I don't think however these are avaliable, certainly not from Ford I should not think.
Can you not repair/have repaired the rust thats there?
Martin