This is a graphics cards chart that shows where cards fall in order of best to worse and compares Nvidia to AMD as to what level the cards compare at. The 560Ti is two levels above what you now have and is it worth almost $500 to do so. Sinse you do have two good performing cards you can wait for the release of the new cards from Nvidia and see what those prices will be and there will most likely be some good price reductions , rebates and/or sales. If you were going with an upgrade now then I would be going with a 570 or 580 in order to see a good enough performance increase. But that's just me and what I would do , your budget might be different from mine. I'm not sure that you would be happy with the performance increase in going from two 460's to two 560Ti's. If you did go with two 560Ti's then you might want to look at this card;
If you were upgradeing to the 448 core version I would say yes it is worth doing , but I don't want to say yes to the regular 560Ti and you get them and end up not happy because the performance increase is not much. Then you will be unhappy with me for agreeing with you to get the regular 560Ti's. I would rather see you get the 448 core version , but I can certianly understand if you don't because of the price being too high.
It is your computer and your money so in the end you are the one making the choice of what to put in your computer and it shouldn't matter if I agree with you or not. I'm just one person and my opinions are based on my experiences and knowledge and it's not my computer but I would like to see you get a good upgrade and not a soso one. Who knows you may end up likeing the choice of the regular 560Ti's.