I had the same motivation to run Mint LXDE on my old laptop. I'm running it in a VB virtual machine, where the standard Mint edition had problems with gnome3 graphics. So I additionally installed LXDE on top of the standard Mint. It's running pretty smoothly and did only crash once or twice while shutting down the VM. In fact, it seems to me that this post-installed version of LXDE runs even smoother than the Mint LXDE version, which I've installed on a different machine a few weeks later. But this might be due to different hardware. Anyway, it seems quite stable to me.