Ohh, this is a tough one. I, in general, avoid reading stuff continued on by another author. Would Brandon Sanderson's work be considered a pastiche of Wheel of Time? Not read then though, I fell off that series well before he took over.
I did like Robert Jordan's Conan stories, but I've not read them recently since reading Howard's complete Conan run, they might not hold up as well in a direct comparison. There are lots of Lovecraft imitators, not sure if they can be considered pastiches. Though Robert R. McCammon's "Fall of the House of Usher" sequel was fun, I was still in high school when I read it and my recollection of it is highly suspect.
These days it seems like most pastiches are "hidden" with the co-author illusion. The numerous Tom Clancy spin-offs, etc. Do I like Larry Bond's newer stuff with a co-author as much as his older stuff presumably totally written alone? Hard to say, my tastes have changed a bit. But I think the earlier works were better.
Not read much of the Lustbader Bourne, but they seemed comparable to Ludlum. Gardner wrote some outstanding Bond novels, far better than the later work of Fleming IMHO. But some of this type of stuff is just more modern or more influenced by successful films so I think it appeals more.
Comics are probably the supreme example of the pastiche, characters grow and develop over DECADES of collaborative work. There is a weird melding of old and new, parallel storytelling, alternate versions, and over time the mythology of the characters evolves in odd ways.
