As they’re cheap and relatively easy to change, I did the thermostat and cap anyway at about 60,000 miles. Although the old thermostat was quite serviceable, the new one made the car get up to temperature* almost a mile quicker, so it was worth doing.
*gauge halfway, anyway - it’s not properly hot (stat open and top hose getting warm) until a couple of miles later, but the gauge won’t show you.