I have seen lot of bloggers have a misconception About expire domains.
They think Domain which have High Da and Pa are most authority one But Google loves non dropped Google index domain (aged domain) rather than new register domain with lot of links.
If you are purchasing expired domain that are dropped already then you are wasting money because after the expired date domain is register as new one.
So if you are on affiliate then purchase aged domain in your niche that are not dropped and see results.
Don't believe me go and check age of most of affiliate site.