I'm not sure about live series cards. I'm pretty sure cover athletes will go up. I don't think there is any other way to obtain them outside of pre-ordering yet, and there is a 96 Joe Mauer collection reward attached to them unlike the other pre-order pack. Demand will increase, and the only supply will be those who pre-ordered and might not sell. Long term I'm sure they'll go to quick sell value at some point, but short term I expect them to go up a lot.
If I had stubs I would invest in them, but all of my stubs are tied up in other cards at the moment.