Have to say, of that 8,000 many were 'duplicates', e.g. pence copy, MJI copy, etc. But in respect of your point above, many were the kind of comics you would only buy if you were a completist. Only a completist would buy 'Marvel Adventures Spider-Man' for example. No regular comic store would go out of their way to stock that title. As a completist, that's where Mile High came in handy as they have the resources to keep the drek in stock.
Extreme completism I wouldn't recommend. If it could go back, the money I spent on every issue of 'Power Pack' with Spidey in for example I would put towards a key, or just any other non-Spidey book title that I liked the look of.
If you look at the 40 or so variant covers to the ASM v3 #1 relaunch, while it was cool to have the set, most of the covers were poor / done for the sake of it. You stand back and look at them all laid out, they look great as a group, then it hits you you've spent £1,000 on 40 terrible covers.