Not sure why Lemond chose 25.4, but I do have a few road bars that are that size as well.
Unless you really really really really want a specific stem that comes only in 26.0 or 31.8, I can't think of a good functional reason to change out the bars. There are lots of stem options that will give appropriate rise with a 25.4 clamp diameter. If you want new bars, that's a different question.
I am choosing Thomson stem and was trying to decide if I should get the 25.4mm or the 26mm (and use with a shim) to get the most cross-bike usage out of the one stem. I have a fixed gear bike that uses 26mm bars.
I think the larger diameter tubing can be stiffer, but smaller gauge. So the bar is theoretically stiffer, yet lighter. I've found no functional difference in any of my bars, but I can barely flex spaghetti.