I know this would wreck their whole sales strategy ("X amount of time left"), but I wish you could go back and buy an old bundle for something like double the average or whatever made sense for them.

I doubt the developers want to have their games available permanently on sale. So unless you really want to pay $50-60 for old bundles, it won't happen.

It makes more sense just to buy the stuff you want directly from the developers. Or wait for another sale.

They pretty reliably give the previous bundle for free if you pay more than the average for the current bundle, but don't bet on it.