Regarding sounds, I don't think he's going way over board, but that's your opinion. The sounds in GT5 are crap compared to FM4. Hell, I think FM2 sounded more realistic than like 99% of what I've heard in GT5. I do have a few cars that I like the sound of (pre whatever patches that changed most of them) but they don't sound like the cars. The ZR1 RM and very powerful Camaro sounded great but neither sound like the real thing would sound like.
I mean a VR6 equipped VW in Forza has the VR snarl. The VTEC sounds at high RPM. The high boost cars sound as they should. The vettes, although lacking the ear shattering and shear ballsiness bass to them still sound like vettes, even modified. But the vast majority of cars in GT5 sound like a digital blender had a baby with a digital vacuum cleaner. The crashing bumps are horrible. The tire squeals you can't make anything out of it. This isn't saying that FM4 does it dead right 100% of the time, they just do it significantly better than GT5. In FM4, I think they added more 'hollywood' effect with the crashing sounds and upped the engine volume on many of the stock cars but I'd rather want that then the same vacuum sound. I think the only thing in GT5 that I've experienced which sounds realistic is the 787B at idle, but it was rather low sounding in my book.
Regarding modeling, PD's premiums are 1 step above T10's but to be honest many of it is wasted. Like I really don't car that the back seat stitching is modeled in. Premium cockpits do look like they are modeled better, as do the overall cars. And I wouldn't mind if PD grew their team or outsourced work and still kept a high level of quality. Keeping everything in house and refusing to outsource is a mixture of arrogance and stupidity. PD's loss really in terms of sales, as is the gamers' who want more, like me.
Regarding driving is a different story... That comes down to the game's physics and the data in which is put in. Just look at the VW Beetle premium DLC which weighed heavier than the real thing.
And it doesn't stop there... PD taking their time still resulted in an Audi R8 having the wrong engine in their model, patched now but patched in well over a year post launch.
Just my 2 cents