I went and picked up four new springs and a complete new wet bolt kit from the local Six Roblees' this afternoon. I tried for upgraded springs, but the stock 1,750 pounders are the most heavy duty you can go on this particular spring length.
I figured I got at least 40K miles out of the original springs with only one broken one towing near max capacity most of the time, so $350 to buy all the parts to rebuild the suspension seemed like a reasonable deal. The guy helping me at the store looked at my spring after I told him it snapped on a relatively small bump and pointed out that there was rust down into the steel along the fracture, which means it had been cracked for quite some time and I was lucky it decided to let go where I could easily drop the trailer instead of the middle of nowhere in Idaho or Utah.
I spent some time today looking at floor plans of the newer trailers and I can't find anything I like better than mine, so I guess I will sink some more money into it and keep it around awhile longer.