Our decision to take steel was based on a number of factors, but one of the more persuasive ones was the ability to do deck repairs and hull damage in far-off locals (there's welders everywhere, but not good glassers), and the very simple observation that a large percentage of "expedition yachts" are aluminum or steel. We know we've got a heavy boat (Saturday's weight on the crane with empty water and full diesel was 29,500 lbs.), but we have confidence in her, and attitude is really a large part of successful sailing.
Even so, I am doing some extensive modifications of the tankage to get her a little stiffer, as I feel that I can get a bit more out of the sail plan if I lower the CG a bit, not to mention the motoring range extension I will get with a third fuel tank.
Keeping on top of rust is an issue, yes, but not an onerous one if you try to keep a clean boat. For some of the concerns involved, I would suggest reading "Metal Corrosion in Boats".