Head gaskets from those years are your biggest worry. Besides that, they're great cars. Perfect snow car, the AWD system is amazing. Though i must say, don't skimp out on your tires. My previous Subaru had three different sets of tires on it during the 9 years I had it (got totaled in an accident), the one set of tires that I went cheap on really made a big difference when driving in the snow. The AWD system kept the vehicle going front and back, but it wanted to swing out on turns. I changed those tires for some better ones and it fixed it right up.
I'm now on my second Subaru, and I can't wait till the original tires are worn enough to warrant changing them. Again, the AWD helps go forward and backwards, but if I take a turn quick the back wants to swing out (though the stability control helps to limit it, but I still want better tires).
Treat it like any other used car, try to find one with as much maintenance documentation as possible, change out the fluids when you get it, and check if it's got any head gasket issues or if its been replaced. For certain years, if you used the Subaru coolant conditioner Subaru extended the warranty on head gaskets to 10years/100k miles.
