No, I think it's a given that GT7 on PS4 is going to be a better game than GT6. Just one aspect, tesselation being built into the PS4 hardware, rather than needing to be coded into the game engine, will be one less burden on the engineering team. And possibly work much better.
A more comprehensive, powerful GPU with access to all kinds of fast ram is going to make possible a lot of lighting effects on the fly, so that every track can have day to night transition, and artists free to paint scenery right without baking in shadows and lighting to help the system out.
Weather effects require some tricky calculations too, especially when you have a number of cars being simulated at once, and likely more than the 16 car limit of GT5.
Online clubs and leagues may be able to race 16 car fields or more, depending on how Gaikai's cloud helps with juggling all those players at once with low latency and hiccups.
Sound and Standard cars and tracks aside, most of the criticism of GT5 revolves around muddle-headed thinking. The completely unnecessary XP leveling system, the paint shop with NO Paint, incomplete online build, and... well, everyone has their gripe points. And I have to believe that the false starts GT5 had, coupled with "taskus interruptus" of GT PSP, the damage model we deplored that was scrapped, and SONY insisting that 3D be wedgied in, didn't help with that. From everything Kaz has said, the team has taken our criticism to heart, and GT6 sounds to be a much more focused Gran Turismo like we're used to.
And I have to remind people that this isn't the first Gran Turismo. Much of the team has been there since GT1, and I see no indication that they suffered some Big O-like mass amnesia. They have a legacy of producing some darn good racers, and you critics can balk at sales figures, but the fanbase has clung, dare I say it, tenaciously to this series, so they're doing something right to have such long lasting high selling appeal. And GT5 is still selling, so not everyone agrees with your assessment of suckage.
I still believe in Polyphony, and Kaz, and I'm not alone on this, and I'm pretty sure positive outlooks are still allowed around here.