Silicone on plastic laminate. We used to build custom laminate countertops as part of our custom cabinet sales/installation business. After the countertop was installed, it was cleaned well, then a food grade spray silicone was applied to the countertops and buffed up with a soft cloth. It protected the countertops from scratches and stains from the other construction workers. We sold cans of KEL silicone thru our company. You can also buy food grade silicone like CRC brand (sold in the electrical section) at several hardware/home improvement stores. I periodically wax my laminate countertops with automotive silicone wax/glaze.
Solid surface materials... you need to know what material your countertop is made of (what brand) as not all solid surface materials are created the same. The only material I am very familiar with is Corian. We were authorized dealers, attended educational seminars at a premier Corian Fabrication Facility in SC and David learned how to work and install Corian from the same facility. We had over 15 years experience with Corian. I occasionally use a silicone car wax/glaze (wipe on/ buff off) on our Corian on the food cart (exposed outside 24/7). Our counters get used hard and suffer alot of abuse. They are due for a good mechanical buffing. Below is a link to how to care for your Corian. If you have Corian, please read it and download the PDF manual as well. The minor scratches are typically perceived as "patina". Difficult to impress upon customers that Corian, or any other synthetic countertop material, is not impervious to scratches, etc and they will accumulate them. The material will not stay looking like "new" without being buffed unless you never use it (and I have installed high end "gourmet" kitchens that were never used).
Caring for DuPont? Corian®
As for what damage putting urethane all over your solid surface material... perhaps you had better ask the manufacturer.