Yes. At least if you want to play on anything bigger than the small maps and/or want to run other programs in the background.
On larger maps when loading up a game, scrolling around, or switching to world view, there is a huge difference between 512MB and 1GB that I've noticed. Not really much difference when stationary. I still end up using quite a bit of pagefile on a Huge map later in the game with 1GB even though (~700MB used by CIV), so all the way up to 2GB is probably going to be paying off with better performance.