thier was a guy on ebay selling miata sytle bars for a 2nd gen vert. but yes they were for looks only and if you ever rolled it would probably be the thing that kills you. I am getting the Kirk bar and once I have it installed I might make some changes to it once I see how much it affects the targa top going up and down.
The Kirk Racing roll bar install reduces the rearward seat travel by about 2 inches and appears to affect the seat back recline. So if you are tall, you might consider if you want to sacrifice the 2 inches.