Your kilt should last a life time (or more) if cared for correctly .It should be hung (not stored flat) The more evenly the weight is spread during hanging,the better .A specialized hanger called a ,'clamp', or 'grip', hanger should be used. The most ideal sort would have four clamps on it. You should never use the kilt s hanging loops for a prolonged period as the garment will sag and deform..For long periods you should hang your kilt as described in a suit carrier and in a dry atmosphere.Some protection against moths should be used but better you use a cedar based product rather than the camphor/napthalene products, that will cause the item to smell.These produsct also have some health and environmental concerns surrounding them..
A kilt should definitely NEVER be wet washed. Spot washing with a suitable detergent for 'delicates' is recommended for local stainng. The process should be done with a dabbing rather than rubbing motion.It will generally be the front 'apron' of the kilt that will get dirty and so this can be done fairly easily in comparison to the complexity of the pleated rear.
In the case that there is widespread soiling and staining,the entire garment can be drycleaned ,BUT a specialist in this field should be sought out as it would be beyond the range of skill or knowlewdge of the