He's mentioned the effect that Berkshire's brand reputation has on investment returns in his annual reports. It's substantial, but not in the way you theorize.
Basically, Berkshire's reputation for 1.) being financially stable through good times and bad 2.) keeping existing management and place and 3.) being able to allocate capital from cash-rich but growth-poor businesses to growth-rich but cash-poor businesses makes them a "preferred buyer" for many strong private companies that are seeking to get liquidity for themselves or family members but don't want to kiss their baby goodbye forever. That a.) opens up dealflow to Berkshire that would never think of selling to other private equity firms and b.) gives them a good price on the deal, since the owners are not seeking to generate a competitive marketplace of bidders that might drive up the price.
Although Berkshire does invest in regular public companies on the open market, that hasn't driven the majority of their returns in decades. Instead, their modus operandi is usually to buy 80% (there was some tax reason why it was 80%) of highly profitable private businesses, and then use the cash generated by those profits to buy more highly profitable private businesses. They only invest in the public markets when there are no attractive private opportunities available, and in some cases they take formerly public companies (eg. BNSF) private. The subsequent share price matters little with this strategy, because the investments are illiquid and just spin off lots of cash from profits.