Okay, I replaced the hose and did the flush today. Here are some thoughts:

PROCEDURE:
1. Line your work area with newspaper or other absorbent material. You WILL spill some PS fluid.
2. Move the windshield washer reservoir out of the way so you can access the return hose easily. (Mine is a '96; I understand the reservoir is a little different in the turbo models.) The hose you're looking for is the one that connects to the bottom of the black plastic PS reservoir.
3. Using a fluid transfer suction gun, turkey baster, or other device, remove the fluid in the PS reservoir and put it in a suitable container for proper recycling/disposal (check local government regulations). You'll get a little less than .25 litre.
4. Tighten a hose clamp on the rubber return hose. Loosen the 10mm bolt that holds down the metal return lines under the washer reservoir and disconnect the rubber return hose from the metal return line. (Have some paper towels in place to catch the spill.)
5. Connect a 3- or 4-foot section of 3/8 in ID rubber (fuel) hose to the metal return line and run it down under the car and into an empty 1-gallon container. Make sure the container will not tip over when fluid starts to squirt into it. (Note: I had the front of my car on jacks when I did this, based on another post that suggested the PS pump wouldn't pump as hard if the wheels are off the ground when turned. In retrospect, I don't think it made any difference, although it did make it easier to fit the 1-gallon container underneath.)
6. Fill the PS reservoir with new fluid. Get your additional containers of new fluid ready to pour (caps off, within reach).
7. Have your assistant start the engine and turn the wheel back and forth quickly while you replenish the PS fluid in the reservoir. WARNING: It will pump out as fast as you can pour it in, so be prepared to go through 2 litres in under 20 seconds! You don't want the pump to run dry, so shut off the engine before it does.
8. Reconnect return hose, remove clamp. Replace windshield washer reservoir. Fill PS reservoir. Start engine, turn wheel side to side, filling reservoir as needed. Take test drive and fill reservoir as needed.

FLUID: I used 2 litres of Febi PS fluid (about $8/litre) for the flush, then refilled with part of a third litre. The 2+ litres of waste fluid was gross. The new fluid in the reservoir is clean for now, but I expect to do this again in a year or two. An alternative approach is to use a larger quantity of cheap PS fluid ($2/quart) followed by 1 or 2 litres of Febi or MB fluid, but please be cautious. Because the fluid foams as it is pumped through the system, a 1-gallon waste container can catch only 3 quarts/litres before it overflows.

UBERWGN'S FLUID SWAP METHOD: In principle, this would be a fairly good method (it's certainly easier than the flush I described), but its efficacy depends on the percentage of the system capacity contained in the reservoir. In this case, the PS system holds 1.0 litre total, with a little under .25 litre (let's call it .2 litre) in the reservoir. If you suction/refill/drive four times, and assuming perfect redistribution of the crud each time, you'll remove about 59% of the impurities. With five cycles, 67%. I like to think the flush does better than that, but of course it's a tradeoff. If the reservoir held 50% of the system capacity, Uberwgn's method would definitely be a good choice, as four cycles (2 litres) would remove 94% of the impurities.