The banknotes would not be worth collecting as they are all the same across Europe..
The coins do have different backs and they brought out lots of commemoratives in the 2 Euro size.
The Greek coins are easy enough to spot, instead of having "Euro cents' written on them the have "Lepta" or "Lepto".
There are plenty of sets around so I don't think they will ever be rare, The Drachma coins were never that collectible either but there might be enough of a story behind a set of Greek Euro coins to make them more interesting.