I agree with you on the warranty - if I was buying privately used I'd see this as a massive plus against similar (likely more expensive) cars on BMW's approved used scheme.
Likewise it's got all the important spec options (Xenons, Pro Nav, Auto, HK audio, etc) that will appeal to a wide audience of buyers. The beige interior is more of an individual choice, but even if it wasn't my first choice I could live with it more than I could live without the spec options mentioned. On the remap, personally I'd get the car flashed back to standard rather than misrepresent or put potential buyers off - how does this affect the RAC warranty? Presumably similar to BMW's own warranty and would void an engine related claim if they knew?
Good luck with the sale if you go ahead. To benchmark your price, why don't you stick the car on tootle and see what potential offers you get from trade buyers. Costs you nothing and you're under no obligation to sell, might surprise you if you get the right trader who has a buyer of their own lined up. 320d xDrive with low mileage and high spec will appeal to a lot of people for the blend of performance and economy
