Emissions is something I didn't think of, but are V4s more efficient than inline?
Sound cooler alright.
They also, depending on their configuration (90, 45 ect) should be worse for mass centralisation & sur flow (downdraft being the most efficient)
Big question is though, hear driven cams (VFR) of chain (Honda's before the VFR when it all went horribly wrong) / belt (Ducati)