If we're including MPC's 6. If we don't, I have one, a lowly TR-505.
All my MPC's were dead cheap so I went overboard. But Ibunshi is pretty much right mastering any one, in this case MPC, is going to somewhat negate the need for other ones, unless another MPC has a feature or features that would really fit your workflow or how you'd like to change your workflow.
If I had the chance to do it over again I would have stopped at maybe 2 MPC's and if I got other drum boxes would go for stuff that are different yet complementary to an MPC like the Elektron gear Ibunshi brought up.