We've ordered thousands of BPOs over the years, and I tend to agree about the overall value accuracy but we're not always looking for value. We're using BPOs more to look for property descriptions and photos so that we can make a potential renovation judgement or to validate values we have from other sources.
We also have REO agents in specific locations where we buy often. And since they're dispositioning assets, they tend to give us better quality BPO reports.
Also when you're reading a lot of these reports you can start to tell from these descriptions who is good at BPO's and who isn't - and who to use again. We'll also will call the BPO agent sometimes to confirm data on it to get more details(another way to figure out the quality of the report pretty quickly).
Also keep in mind that bad BPOs can make you money too, like when the bank is using that for example, and you have quality boots on the ground giving you a more accurate value. So, I've found it works both ways!