I agree with some of the sentiment of what your saying, if I didn't have the chance of the grille at a reasonable price I wouldn't be considering it. How much you pay is your business, please don't think I am commenting to for that, however, the S3 front end looks mint, why change it? i mean, even the 'reasonable' price is going to be expensive enough for a part of that nature (i.e. popular) so spend that on the mapping, exhaust, mods for future mapping, etc surely?
However:
i) Its still a 3 door so will never really mimic an RS3 look wise, 3 doors just ain't enough!
ii) It doesn't have the same bumpers or exhaust outputs, agreed.
iii) It will be firmly badged as an S3, not an RS! Phew! Now I can relax! LOL.
iv) as it's black I don't think too many of the mods will stand out to anyone other than the trained eye Its not just 'Black', its only Panther Black which really is a superb pick. Again I could not afford the colour I wanted more the wait till Feb for it either but that was a Blue, however that Panther is really good.
Hopefully by S2+ it will have the power of a basic RS3, but I'm under no pretense it's anything else. Its purely a case that some bits came my way and I've taken the option, initially I had no intention of going out to build a fake RS3!