I've had a bunch of those engines, including the one that I put in my old Porsche, and I LOVE them.
The bottom ends are very strong, almost indestructible in fact. The only place they give trouble is with the heads. As stated above, you must stay on top of timing belt maintenance. The good news is they are much easier to work on then the newer TDI engines (we have some of those in my family too) and the parts are inexpensive and easy to find, as close as your nearest NAPA. Having done both, I'd say that a timing belt job takes less then half the time for an old IDI engine compared to the same job on a TDI.
Here is a good forum site for information on these engines:
Welcome to VolksWagen Diesel
As to economy, it's true that they are slightly less fuel efficient than the newer direct injection engines, but they can be bought in good shape for thousands of $ less, and that will buy a lot of fuel
