I really cannot answer that question for you, in depth. Yes, of course it is better, that is why they designed it, but it costs more [a lil bit], and you will require as you say a new mb. A quick search will explain the differences in as much detail as you care for. It comes down to what you use your sys for, and if you , just you, will notice the difference. You would for gaming and CAD work, but never for everyday home pc work like networking, mailing, home accounting, or even for your average picture retouching work.
Comes down to money, and perhaps some sort of pride or satisfaction.
2GB is a fair jump from 1/2GB... and if you have a fast cpu you may notice the difference - your cpu will spend a lot more time doing nothing. I doubt that you are, or want to be, a full blooded gamer so just think a bit about why you are doing it.