Completely agree with everything you said. I was only calling libor risk-free as it is what would be substituted for the risk free rate used in finance textbooks. Technically it's not risk-free but serves as a base return to benchmark off of. Also, most of these bonds pay coupons linked to libor.

Attachment and detachment point are definitely very important. I found a random fed document from 2012 that suggests similar attachment/detachment points for AAA prime vs subprime abs securities (~79% attachment). I haven't looked at it too closely though and I could be missing something. I know spreads are a lot tighter since 2012 and credit quality of underlying loans may have worsened with lower standards. On the other hand, people are a lot better off now that in 2012 (i.e. stock market, housing market, etc).

Will check out Scarcity. Thanks for the recommendation!

[1] http://www.federalreserve.gov/SECRS/2012/May/20120523/R-1401...