Reusing electrical supplies is an option in many cases, but sometimes you just need to junk your old gear and start from scratch. Those obsolete power circuit breakers, breaker panels or other gear may not be worth trying to retrofit if your power needs have outpaced the capabilities of the old system. In cases like these you may feel the financial sting of the investment, but you may not have to simply dispose of the old equipment. Your old system may be eligible for a buyback or "takeout" service for cash or store credit.
Don't just throw that old gear away, call your customer service rep and ask to have your old equipment evaluated for purchase. Power circuit breakers, panels, sub-panels and other items are frequently purchased to be re-utilized. Sometimes the unit itself can be salvaged or it may be cannibalized for parts to be installed in other items. Regardless of the final uses, your old gear may help cut the final price of your new system.