i always wash my ironing board cover when it needs it- i've been using the same one on my large ironing board for 20 years- and the ironing board and original cover were purchased at a barn sale- had been sitting in a back room for probably 20 years before it became mine-
cover has some stains from years of use- but washes up nicely- no damage that makes me believe i need to replace it.
i think my mom's ironing board cover is probably at least 50 years old- she takes it off & washes it when it needs it too. we have both replaced the padding once or twice over the years.