I agree with Yorks_Rider, resale value will depend a lot on condition and also what is out on the market at that time. I hesitated too at the time, then waited until they were 20'% off and bought them new. Never regretted it. It's Beemer, so they will always be expensive, but I find them practical especially with their variable width. Alternatively you may want to think about getting some reckless soft luggage options, though these might require the tail to be used for mounting (unsure).
If you buy used, check the Vario mechanism, they can get wobbly with time or after crash.