Well - the printing on the Poly-bagged Elrond looks (to me at least) to be representative of him during the final battle of the 2nd Age when Sauron was defeated...
![](http://www.bricklink.com/ml/lor033.jpg)
And then the Elrond that comes with the Council set, is like how he's dressed in Fellowship of the Ring...
![](http://www.bricklink.com/ml/lor059.jpg)
So they are technically different.
It's interesting that you mention the Mirkwood Elf set - I was looking at all of the sets for the Hobbit and LOTR on brickset.com and apparently there was a poly-bagged Legolas that was planned but not released. It doesn't look like the minifig was going to be anything other than a re-release of the Mirkwood Spiders set Legolas, but the accessories he came with were kinda neat - like a target practice thing. Anyway, in the instructions for that set, there is a typical Lego picture that shows what you can make if you combine two sets. In this case, it's combining two of set 79012 to make a larger Mirkwood set.
It's not something that I plan to do right away, but I am very tempted to get at least TWO of the Mirkwood Elves set just so I can make a larger "fort" with a tower at each end.
In case you're curious about the cancelled Polybag Legolas the instructions can be found here:
http://cache.lego.com/bigdownloads/buildinginstructions/6073659.pdf