The answer depends on the several factors that determine the relative economics of the reuse of existing space equipment vs. building new equipment: type of demand use cases for space travel, type of reusable equipment, fleet size, trip frequency, etc.
Here's a NASA research article that lays out the factors in detail: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20160013370.pdf
ItPer a recent article (https://www.forbes.com/sites/quora/2017/01/05/why-doesnt-nasa-develop-reusable-rockets/amp/) that quoted a NASA official, it was less expensive to reuse SRBs for the space shuttle (due to the frequency) since the space shuttle had a high frequency of trips.