No doubt about it, the G3 Ti200 is a better card than the G2 Pro.
However, many things come into the picture when talking about is it worth or not.
First, what CPU do you have ? On the latest CPU, go with the G3. But on older CPU, G3 may be overkill since the CPU will limit you.
Is it worth then paying for a G3 you don't benefit from, because of your "limited" CPU ? Choice is yours.
Also, what size is your monitor ? What is the resolution you typically run ? According to most reviews, teh G3 Ti really shines in high resolutions, 1280x768x32 and above. If you monitor is small, or can not support such resolution, then again, the benefit or a G3 over a G2 is minimal.
Th GPU market moves so fast, that I wouldn't buy anything I can not benefit today. I wouldn't pay big bucks now, for something I would eventually benefit in the futur. By that time, new products will on the market, with better performances for less money.
To me, it all comes down to : what is your config right now ?
Remy