The dongle for the PaperClip word processor plugged into joystick port 1. It read bits 0 and 1 from the dongle and wrote bits 2, 3 and 4 to control it.
Keyboard interference probably wasn't an issue with this use case.
There were several cards, in the mid 1980s, based on use of 64 KiB. Except that it was usually not to use full 64 Kib, but to get RAM at the right location some (game) program wanted it.
For example this page shows three different boards of that time frame.
The main issue with RAM in the VIC20 is less the amount of RAM, than that its use swaps around, ...
Common 8-bit CPUs have sixteen address lines and eight data lines
appearing on their own dedicated pins on the chip; these are connected
in various ways to other devices in the system to form the system
address bus and data bus.
Memory and other devices have their own sets of address and data pins,
which will be connected in various ways to the address and ...