This is the type of 4-letter .com that doesn't really have many end users. However, for the sole reason of it being an average-quality 4-letter .com, I'd say it's worth low $xx. If I had pblx.com, I'd put a coming soon page (built by me, not a parked page), wait until September, put a nice little ad-supported arcade on it, submit it to a few arcade lists, and let it run mostly on autopilot.
I agree with xtmx, I dont see much worth in this domain but obviously good for future. Hold if for several more years with you if you are not looking to develop this. Some day it will worth good amount.