Funny how we find ourselves at the same place, but from different directions. I actually had all of their albums on cassette in 1986 (Tales of Mystery - Gaudi), but traded them off decades ago when I switched to CD. I never replaced them and probably went 25 years without thinking of A.P.P. until I saw a post for "I Robot" on this thread about a year ago. I listened to the samples and immediately placed an order for it on Amazon. My tastes in music have changed considerably since the mid-80's, and I doubt I'll collect all of them again, but 3 or 4 of those albums are "must owns" 
The Alan Parsons Project is one of those artists that I have owned the greatest hits albums and a few of their other albums like Ammonia Avenue and Tales of Mystery and Imagination, but had no real interest in picking up any of their other albums even though I liked the music. I rarely find the CDs used, but I did pick up four of their other albums on vinyl. Should be able to play them soon.