Aluminum from 20 years ago was pretty rough, from what I've read. Current aluminum is pretty nice. My main race bike is aluminum (2012 Allez E5) and it's fine for 100 mile days. Aluminum is experiencing a mini-renaissance, with Cannondale, Specialized, Scott, BMC and Jamis pushing their aluminum lines as serious alternatives to carbon, rather than just cheaper versions.

Steel is more a niche market. It's harder to make a steel bike that's stiff in the right places, compliant in the right places, and lightweight enough to race. Steel makes a wonderful non-race, "endurance" style frame that weighs a pound or two more than carbon or aluminum, and this is where the market for steel is. I did my last charity ride (75 miles) on my '87 Centurion Ironman, including a half hour of hammering with the local racers, and it was comfortable and handled well. Centuries and gran fondos are perfect for steel.

Since it's a niche market, there's much less of an economy of scale in production, so steel costs more. That said, you can get a pretty nice frameset for ~$1,000.