LP -- having a brain that constantly seeks symmetry in all things (must be the German side of my family gene mix), I guess it never occurred to me to just upgrade the rear.
Actually, I was intending to sell the old wheels -- easier to sell a set, than just one, it seems. Still, getting just one wheel, and a darn good one, is certainly an option. Good idea.
Laced 3 cross? What does that refer to? I'm not too savvy on wheel builds and lacing -- I presume that means a method of weaving the spokes? Stiffer that way?
From some of these comments, I am thinking that perhaps just re-spoking my existing rear wheel with thicker spokes might be an easy way to go. Those wheels have certainly held up very well, given my weight, frequency of riding (about 4 hours per week; May to November) and some of the things I bash into with them. I've mentioned before -- the trails here are pretty smooth, but there are some that are littered with roots, with the odd rock garden thrown in to make it interesting. Like I said, I have only had to re-true the rear wheel only once in 3 years; the front maybe only twice. Pretty good record, I'd say...