Partial answer (not touching the economic issues)
(I asked an older question about the economics here myself Documented economics of STS Solid Rocket Booster reuse? but have not received a satisfactory answer)
Shuttle SRBs were built out of segments and reuse was at the segment level.
This illustration shows the 11 segments that made up a single booster. (The red letters are personal nomenclature).
The boosters came from the factory in four pieces. The two center pieces had two segments each. The forward piece had three segments, and the aft piece had four segments. The pieces were joined at the launch site and further outfitted to put together a complete SRB.
See the references for image and data sources and caveats. This answer only addresses flights of Shuttle Program SRBs, not ground tests, Ares-1X, or SLS.
How many were re-used?
643 unique seqments flew in the Shuttle program. 539 segments flew more than once.
What was the record for most flights for a single SRB (if you can
count refurbishment and necessary parts replacement to still be the
Two segments share the record of 12 flights each. Both are forward cylinder segments. Their serial numbers are 078 and 056. This graphic shows where they flew in the SRB for each of their missions with the mission number and left or right booster assignment below.
Caveats and comments on the data used for this answer:
- The flight history of the segments is complicated. Segments were
lost, added, remanufactured, etc. throughout the program. The Space
Shuttle Almanac provided an invaluable table of segments-per-flight.
I attempted to validate this table using the booster segment history
graphics put out by ATK for all the flights I could find. I had a
valuable dialog with the Space Shuttle Almanac author for a time
working out conflicts between these sources. Most of the conflicts
have been resolved, to my satisfaction at least, and the updates have
been reflected in the Space Shuttle Almanac to the best of my
- The history of segments listed in the answer above has been validated
by ATK documents; completely for segment 056, and through STS-105 for
segment 078, so I'm quite confident on the results for these two segments.
- I would welcome any corrections to this answer based on documented SRB usage data!