Hi. interesting question.
Let's look at it a different way.
1st, if you buy GT6 now, You missed a few of the free vision cars and lots of credits.
That aside i tell you my perspective.
I have GT6 now.
I don't buy the PS4 yet, it's €499 if i buy it now.
when i bought my PS3, i got 2 DS3, GT5 and Uncharted 3 in one package for €279.--
You mention that GT6 is around $40,--
Here in my country the GT6 annivers edition is around €48.-- and the normal is around €37.99
I wait, I wait until the Ps4 is cheaper, at least €100.-- cheaper and prefer with a special package ( extra game and extra controller)
Knowing PolyPhony, if you have GT6 on Ps3, you could get a reduction if GT6 comes to PS4, maybe even for free.(hmm, i think i'm dreaming, it probably will cost full price)
Back to waiting untill Ps4 gets cheaper, if i can buy it €100,-- cheaper, i could buy a remastered GT6 and still saved money.
And!! somehow i think, your progress is saved online, so if GT6 comes to PS4, i believe ( not sure!!) you can continue on your PS4 where you left on the ps3.(*)
Also i want to wait if GT7 becomes the game they promise, Gt6 is nice and more realistic but was a little dissapointing.Don't get me wrong, i like the game very much, but still miss some things.
There is only one catch, i have to wait for the price to drop.Could be a year, maybe 2, maybe three.
I got my Ps3 in 2012, so i waited 6 yrs before i bought my first PS3.
(*): There was a credit glitch once in GT6, but only in update version 1.01.
I tried that, did not work anymore in 1.02.So all my credits are legal ( i hit the 50million mark months ago)
I even deleted all game data and all savegames ( backup and normal save)
Always, but always my current savegame came back onto the PS3.So the current savegame for GT6 is stored online or secretly somewhere on the ps3, my guess is online in your psn/GT6 account.
