the last time i had an expired summon was back in 2005 or 2006. and as far as i know, not very sure of it, the expired date in the summon is for you to make the payment, once expired, you will need to attend court to settle it.
i would advice you to pay the summon before it expired, or if you want to appeal, make it before the expiry date. and if it is already expired, then i am not sure you can still pay or not, but if i am you, i would definitely check it out at the payment counter or the traffic police station immediately, and pay it if still able to. no point dragging yourself to the court for the mere sake of rm300, it will be a true hassle, unless you are sure you did not make the alleged offend and you have the proof. that's my opinion.
btw, i also do not know there is runner to pay traffic summon? can share some info and contact details?
might be useful. but for me, i will first try paying online "if the summon is not expired yet".