I haven't sieged for while, like six months or more, but I noticed a huge increase in crash after the previous festival. At that point everytime I change something like in my action bar or a price on AH item usually I crash. Seems to have something related with addons perhaps that alter that savevariable.lua on documents folder and the last two events, since I haven't changed my addons in this time.
Well, if you have elebenty-seven different addons installed, each one of them is going to use a bit of memory (system RAM), some more than others. Considering that as a 32-bit program itself, RoM can only directly use or address data in the first 4GB (give or take) of RAM, regardless of how much more total system RAM you have installed. So, if you don't really NEED several of those addons, remove them and free up some RAM.
Related to hardware, players with 4, 6, or 8 core CPUs are in no better shape than those with dual-core CPUs (other than overall clock speeds). RoM is old enough that, at best, it can only utilize a maximum of 2 CPU cores--it can't really multithread. IF it uses a second core at all, that's accomplished by the OS, for the most part, not the client application itself.
I've also found--for those of us who leave our computers running 24/7--that even with Windows 7 it's a good idea to do at least a weekly reboot. As an example, I did a restart yesterday afternoon. In the late evening, I was able to switch toons (same account, natch) four or five times without crashing. This included several trips in and out (both toons) of their respective houses, based in Varanas.
You can mitigate crashes. But you can't completely avoid them.