To go a little further into the multiple Core Sets thing;
With regards to Core Set cards being obsolete over time, that's certainly possible. It also depends on what level of play you're looking for from this game. If it involves any kind of organized play, be it friendly leagues, or a big tournament, you'll probably have a tough go of it in the immediate future as there will naturally be people with 2 Cores out there getting more reliable card draw.
That's also the next point; reliability. You can only have 2 Emperors in your deck (for example) at this point. On a minimum deck size of 50 cards, that's not even the best guarantee you'll find him in your game, but you're twice as likely to draw into him at some point vs only having one copy of his Objective Set in your deck.
For some cards and Objective sets, that's by design, but when you are trying to build a deck strategy around a few key cards, you'll want to maximize your ability to draw into them, which helps the deck play more reliably versus being more luck driven.
Down the line, unless they start reprinting Force Choke and Force Lightning into other Sith Objective sets, you'll probably still get a lot of utility out of the Vader and Palpatine sets in your Dark Side decks for a while. As well, think a little deeper into those traits on the Objectives. There's "Coruscant" on Heart of the Empire. It doesn't interact with anything other than the Defense Fleet currently, but who's to say that it won't trigger off some other crazy effect down the line?
Good design with games like this would surely involve going back to look at these seeds that were planted back in Core and looping them into new ideas years down the line.
I remember in the Decipher Star Wars CCG, in Premiere, there was a card called (if my memory is correct) "This is Some Rescue!" that would cancel the Light Side rescue card from that set, but also mentioned that it cancelled "Ewok Rescue", which would not see print until the Endor expansion for another 3-4 years!
I know money is precious for all of us, especially if you're into keeping up with a few expandable games, so $30 might be at a premium, but I highly recommend the second Core to get the extra Objective copies. It keeps your options open, and lets you make more reliable decks.