Do wallets always require a private key to spend coins? I recently imported a very old (2012) bitcoin qt wallet address to a new blockchain wallet, but since it's imported, the coins are "watch-only." i was hoping that i could simply send them from my old wallet to my new one, and then i'd be free to spend them. i attempted 1 relatively small transaction as a test, and it broadcast to 4 nodes, but never got any confirmations after a day or so. my transaction fee was set at .01 (about $48 at the time), so i'd assume that a low fee wasn't the issue. i eventually aborted the transaction, and decided to try again with a newer version of that wallet - one that would actually be able to sync the entire blockchain. so that's what i'm doing now... just waiting for it to sync. 

my new blockchain wallet won't allow me to spend my coins without a private key because they're "watch only." i found a lot of stuff from way back when that i thought was (or should have been) my private key. various passwords, a 6-word (no, not 12 words) recovery combo (which were not random - i chose them), and some long gobbledygook that looked like a private key (found in a jason file), but none of them worked. 

all this to say that my old bitcoin qt wallet never asked me for my private key, and as i had mentioned, my attempted transaction was broadcast to 4 nodes, which i'm hoping someone can confirm means that either a) no private key is needed to complete a transaction from that wallet, or b) the private key is saved in the app (possibly from way back when it was originally installed). of course "c" would be that the transaction was not, and never could have been confirmed, and my coins are just gone forever. can anyone tell me if wallet apps back in early 2012 used private keys? i'm just trying to figure out whether i lost mine, or if there never was one, and therefore don't need one.
Yes, all wallets have always used private keys. They're what prevents other people from simply going and spending your money, they're used to make the authorisation signatures in a bitcoin transaction. Your best bet is to just use Bitcoin Core to load the wallet.dat file rather than importing it into a third party service. 


  all this to say that my old bitcoin qt wallet never asked me for my private key


The private keys are part of the wallet.dat file and are never user facing in Bitcoin Core.