I have played around with designs for spoilers and rear box cavities, and I have not yet come to a conclusion or built a final version (only in the mode of "cardboard aided design"). But I'll share these pictures I took this morning when I arrived at work, since my 1998 Coupe is very similar to your VLX.
Driving to work, the car got a light misting in the last two miles, stop and go traffic and then speeds up to 45/50 mph. Here are the water traces on the roof and rear glass that were left when I arrived at work.
I think the traces across the rear show a lot of turbulence.
And here is an older image, in which a morning mist had left my tufts pasted to the car in a trace of the air flow:
My sense is that the rear turbulence cause by the too sharp angle of the rear glass and c pillars would be tough to reduce very greatly at the speeds we usually drive, unless you built a Kammback.
But I still want to try spoilers and such, so I am game to see what you might attempt and test.
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