Is it a good idea to invest in cheap headliners right now (kieboom, sixto, hamels) or will they stay this price? What about live series? And lastly what's a good price to buy the 5th inning bosses? Thanks!!
I don't think that headliners like that will ever see a big spike in price. Not only are they becoming more irrelevant with cards like TA3 surpassing them, but they'll probably still continue to pop up in these flash sales where you get a guaranteed headliner diamond.
The only thing that may spike them a bit is the eventual Honus collection, when they will become relevant for a bit, but it wouldn't be too long and I wouldn't want to tie up stubs in cards that cost 20k, I think they have further to drop
As for the bosses, that's anyone's guess, I'd wait at least until they drop another 5th inning player program and see where prices are from there