I'm telling you that four matched tyres will give a better balanced car than two and two mixed, it really is as simple as that. Will they give more grip? Depends on the tyres, more than likely not, but it will be more stable and that's the key. I'd hope that no-one is daft enough to run tyres that cheap/nasty on their pride and joy, and really the lowest I would be looking to buy would be tyres around the T1R/452 quality. Personally I wouldn't even go that low, but they are at least a known quantity and a quality brand.
Tbh if people want to read all this and still run mismatched tyres than they can go right ahead, just please don't expect any sympathy from me when car meets ditch/Armco/tree. If you want to take sensible, logical, reasoned advice from myself that Nissan themselves agree with and ignore it, then that is of course your prerogative.