You should still be able to get good money on the used market for a launch PS3 (even when they're busted). Basically, once you sell your old PS3, it shouldn't cost you much more to buy a new Slim than it would have cost you to repair your old PS3. That's why when mine went bad, I didn't bother fixing it. Sold it for a good chunk of money (and even told the person I sold it to that it had YLOD-ed), and bought a new Slim without much of a loss. Hell, even Gamestop used to buy YLOD-ed original PS3's for a decent chunk of change (around $100); not sure if they still do.
And, personally, if I still had a working 60gb/20gb PS3, I'd sell it. Those things are ticking time bombs, and after selling it, you could probably come out ahead even after buying a brand new Slim replacement.
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