why some solids are more valuable to acquire? Like solid 8's or solid 7's.
Because they are just popular, are "lucky" numbers or are culturally significant. There is a lot of personal, subjective opinion in play when determining how "valuable" fancy serial numbers are.
In Memory of Crazyb0
12-26-1951 to 7-27-2020
In Memory of Tootallious
3-31-1964 to 4-15-2020