Raspberry Pi is a very interesting product, but with 8 GPIOs I didn't even consider it
Are you not counting the serial, i2c, and spi pins? Nor the SD card, external memory interface (with 256KB memory attached), (HD) video, sound, ethernet, or USB? That's 8 GPIOs plus four "buses" capable of speaking to multiple peripherals, plus lots of "other stuff", which is pretty much more than the usual arduino...
reconsidering, I still don't consider it a development board.
It's much more a "software development" board than a bit-twiddling development board.
This is what happens with faster CPUs. Physics gets in the way, and you don't get to twiddle GPIO pins at the system clock rate any more. Actually talking to peripherals becomes "expensive" compared to the memory/CPU pipeline. Talking to things that are "off chip" becomes very
expensive. Instruction timing becomes non-deterministic because of pipelines, caches, and variability in memory timing. The usual technique for doing IO to to put the data in a block of memory, point some smart controller at it, and say "go."
What is it you think you would DO with a 1GHz CPU and a bunch of general purpose IOs? At some point, the "problem" becomes defining your actual requirements, rather than just saying you want it all. You can see this in the numerous discussions about 8 vs 32 processors, or (less often) discussions about using board-level "modules" in a product rather than a design based on chips.
There have been a couple of attempts at implementing fast but simple cpu chips, and letting the programmer do all the fancy IO. They have ... fallen by the wayside, done in by the enormous speedups that you get by doing more work within the chip.