Final answer:
To address overheating and debris, installing a new system fan is the most effective solution. It improves airflow and heat dissipation within the system. Blanking plates can aid in directing airflow but aren't as impactful as fans.
Step-by-step explanation:
To mitigate debris reaching components and address occasional overheating in a system, the best solution would be to install a new system fan. More RAM or a new motherboard would not directly affect the airflow or prevent debris build-up. On the other hand, blanking plates can be effective in preventing debris from entering through unused expansion slots and also help direct airflow efficiently through the case, but they would not contribute as significantly to cooling as additional fans would. Properly positioned fans both introduce cool air and expel hot air, ensuring effective heat dissipation.