I like to count my mileage (as an annual goal) as well as my average speed. I also use the mapmyride app and just recently got an HRM, but those are interesting diversions, not really essential. Simplicity is certainly worth aiming for.

As an aside, I am still using an original Avocet 20 Cyclometer that I purchased in 1985. Reads in kilometers only. Still works great, and because of the 4 magnets, updates a lot quicker than modern ones.