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...

And then the Elrond that comes with the Council set, is like how he's dressed in Fellowship of the Ring...

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