I know string cleaning helps tone and with life expectancy with steel string guitars, but does it make a difference for either of these concerns when using nylon strings?
Very gross buildups of dead skin collect alongside frets over time. little pieces of grapefruit and donuts and cheeseburgers cling to the strings. You could live off the scrapings from a fretboard for 4 days after society breaks down. Clean your strings and fretboard.
I know string cleaning helps tone and with life expectancy with steel string guitars, but does it make a difference for either of these concerns when using nylon strings?
I doubt string cleaning affects life expectancy of ukulele strings, but they can get a bit sticky over time from sweat or other residue on your hands. Wiping them down after playing minimizes that possibility. I routinely wipe off the body as well.
Usually you combine cleaning with maintenance when you oil your fretboard. Use the same cloth to clean the strings (undersides too), then wipe them down with clean dry paper towel to remove excess oil.