Please consider that the GTX650 (Ti) has a memory bus of only 128 Bit so the card would barely be able to make use of more than 1GB VRam. I don't know if there are other factors which could negate this disadvantage with more than 1GB. Nvidia said something like that but I never heard anything specific so it could just be marketing talk.
Edit: I just read a little bit more on the topic and from what I understand the ability of a graphics card to utilize a certain amount of memory is dependent on the size of the memory bus and the memory bandwidth.
A common metaphore for the memory bus are the number of lanes on a highway. 128Bit would be 2 lanes, 192Bit 3 lanes and so on.
The memory bandwidth on the other hand would be the speed limit on the highway.
And I also found these specifications by Nvidia which should be more helpful for you:
http://www.geforce.com/whats-new/articles/introducing-the-geforce-gtx-650-ti-boost
According to that the normal GTX 650 Ti is only specified by Nvidia for 1GB Ram which makes sence because it only has a memory bandwidth of 86.4GB/s and a 128Bit memory bus.
The GTX 650 Ti Boost on the other hand is rated for up to 2GB RAM and while it only has a memory bus of 128Bit as well, this card has a memory bandwidth of 144GB/s which should be enough to utilize the larger memory size.
So if you consider a 2GB model of the GTX 650 Ti, then make sure that it is a real NVidia Ti Boost and not a normal Ti with more memory slapped on it.
With that in mind, yes, 2GB VRam would make sence if you buy a gaming card now but only if the card is actually build to deal with this amount of memory and the normal GTX 650 is not to my knowledge. I hope this helps.
Edit: I made a mistake - the GTX 650 Ti boost actually has a memory bus of 192Bit!
