Agreed, these cars can definitely stack up the mileage if well maintained. I've put a donor engine that already had 170,000 on the clock when I bought it. Thousands of miles later and it's still going without problems.
Most of the negative comments I've heard relating to omegas is down to the electrical side of it (masses of sensors). What you have to remember is these sensors are there for a reason and if you don't ignore the EML light and get the problem sorted your engine can go for years. Other makes VW, Mercedes and BMW are all known for there great reliability. I've driven both VWs and Mercedes for many years and when you do have a problem there never seems to be an EML lit, funny that! I like the fact that when there is something wrong with my car I know about it before it gets expensive.
As of the original post, I wouldn't condemn the car to the grave yet but you'll have to put some effort into fixing it. Get a compression test done to see what state the engine is in. Most obvious thing to get fixed is the exhaust which will certainly not be helping the O2 sensor fault. Get the idle valve cleaned as well, these tasks won't cost you much to do either. Check the wiring to the injectors for any splits or loose wires, the wiring can be very brittle in this area and will definitely cause misfiring.