Bugs me that the spoilers are another texture layer (need to remove them in order to install an aftermarket unit in GT Auto) but you can't remove them entirely. Both of the D1 ER34s have no visible spoiler but they're kitted-and vinyled-out, and they have active and adjustable downforce despite the lack of spoiler depiction.
But in general, except for the terribly tuned ricer Blitz Skyline (the standard one) there's no R34 in GT5 without the spoiler.
To be honest I think stock spoilers on cars like they R34, R35 or RX-7 really add to the looks... but to each his own.
+1, Seen show Supras, Rx7 (Fc & FD), Evos, Scoobies, Silvias, Skylines and a R35. Its makes the rear look funny, most of them were designed to have spoilers.