In truth we are all probably grappling with the same things as you, in my case I think these tremendous debts and money printing will one day lead to inflation in things other than the US share prices. The FED are apparently actively trying to release the inflation genie from his bottle and raise rates probably to give themselves some room to manoeuvre during the next financial disaster.
I also keep an eye on the US treasury yields and just wonder how much longer those generous Chinese, Japanese and Belgium buyers will keep supporting US debt.