I'm getting back into bicycle touring after a 20-year absence. For what it is worth, on my first cross-country tour back in the 80's I actually broke two Blackburn low-rider front racks. Granted, I may have been packing more weight up front in order to try to better balance my load front to back, however, the overall weight wasn't anything extreme. After I returned from that tour, I purchased a set of Bruce Gordon chrome-moly steel racks. They were trouble-free on many tours after that, and I have since moved them from one bike to another to another for commuting. Now, I'm looking at doing a tour this summer, and I'll be using those same racks again.http://www.bgcycles.com/racks.html
If I were in the market for new racks, I'd definitely be looking at steel versus aluminum for its durability and stability. Yes, it will cost more, and may be tougher to justify if you do not plan on using them very often, either for touring, commuting, shopping, etc.