I will chime in on the cabriolet market price and say that it's 0-50% higher than an iS of comparable condition. For prospect cabriolet purchasers, the condition of the top and presence of the hardtop should be a big bargaining tool. A nice car with a crappy top is worth $1000 less than one with a nice nice top, and a nice car with an oem hardtop can fetch $1000 more if the owner is aware of the value of the hardtop itself.
Also note that ALL cabrios leak water. Most of 'em from the top of the doors where they meet the top. This is normal, but make sure that this has not allowed the carpets to soak.
Get in the car, close it all up and take a nice, long sniff. If it even hints of funk, get down there and inspect the carpets for moisture.
