Ok, it sucks because without wind tunnel test results, we cannot advance any of this discussion past theory. But I can say that both wings and spoilers have to be sized and placed correctly dependent on the application.
A wing has to be placed in the cleanest flowing air possible, and sized to produce a desired amount of downforce.
A spoiler needs to be placed and sized to reduce as much drag as possible.
Vortex generators, helpful with wings, not spoilers... generally speaking. Once again, if used in concert correctly, you could use vortex generators and a much smaller spoiler, if designed to be used together.
In the above sense, vortex generators are a series of little vertical winglets, in this case placed at the rearmost edge of the roof, above the rear window. They introduce turbulence, and in the boundary layer turbulent air stays attached to the surface better. Placing vortex generators above the rear window influences the air to stay attached to the vehicle and follow the rear window down towards the trunk further before separating.
This would allow you to mount a rear wing lower, or use a shorter spoiler.
Like everything else, though, you need to design it all to work together.
A spoiler is something that you should start with... as every vehicle produces drag and can benefit from the reduction of said drag. Not every vehicle needs additional traction over the rear axle, and thus a wing should only be used once you have maximized your suspension and find yourself still needing traction.