I would have bought it, if they made it for psp. When PSX came out in 2005 they could easily publish an UMD version of it, and with only minor tweaking they could make it run a lot better than the emulated version does. I mean, why didn't they do that? 7 years ago GT2 wasn't even really outdated, if you think GT4's now old as GT2 then was. Since there wasn't any other GT game for that platform every GT lover with a PSP would have bought it, and they would have bought GTPSP as well, being a totally new game released after 4 years. Now there isn't a single living console by sony which lacks gt, and noone should buy GT2.
There's an interesting thing they could do - almost crazy, but I'd find it perfect - : think about a GT1&2 handheld. Not talking about a new console, just one optimized to play that particular games, a sort of Stand-alone. There's plenty of "NES-ON-A-CHIP" china-made consoles that go for 10 dollars, someday psx-on-a-chip will exist (maybe it already does), add 5$ for a 2Gb sd card, 5$ for a screen (production cost), sell it for 40-50 as the "retro GT handheld" and fill your pocket with money without having spent a dollar to try developing neither a new hardware nor a new game.