Having the ability to increase performance without major changes to the surrounding circuitry is often very helpful. Drop-in replacements that are one-clockers or two-clockers help with that, particularly with additional features that only require firmware updates to support those additional features. The ability to extend external bus cycles helps with compatibility with external hardware, and a second data pointer makes some processes much easier, particularly if two relatively separate contexts are involved, as one DPTR can serve one, while the other is used in the other. I'm sure there are many other justifying reasons, but those are some of mine.

I've been happy with the Maxim/Dallas DS89C4x0's for over a decade, and, while the paint is quite dry, they still offer considerable benefit over re-spinning PCB's or starting from scratch. There are things that no other 805x-core MCU's can get done within the same time span, despite a considerably faster system clock ... not terribly many ... but a few, for sure.

RE