I agree with you can never have to much memory. However, the REAL question is this. Do YOU need to? As in, are you having problems that you are hoping more mem will help? If not and it does the job, then really its all up to you. It will be useful eventually. Its like when you get someone getting a computer because there's is outdated. Well, to some that maybe true. However, I've seen people who use it for email purposes ONLY... the problem is they're listening to what the fad is and when they hear that they're beloved mail machine is "outdated" the get irritated and believe the have to order another one. Well, they're listening to sales people and companies. I'll bet you that if they really thought about it then they would realize that number 1. This computer does ALL I need and more for my purposes. Why do I need to upgrade? Because the companies selling these systems tell me that this is old technology? Well, if it does what you want it to do, then guess what. You have no REAL need to upgrade.
If you want it for future use? By all means, do it. Get 1 512 and leave one 256 in. Then in the future you can upgrade to 1gig if needed.