ok, lets start from the beginning; are you wanting to breed EE's, amaraucanas, or araucanas? my thoughts were you wanted to add in another line, to increase diversity and health on amaraucanas. if your breeding amaraucanas it wont hurt to mix in silver EE (recommended), or another similar sized and shaped bird. if you use a similar bird, I would look and try to find what they used to create the breed. determine from there what side of the breed you need to breed back for diversity. breed father to daughter culling agressivly. anything over the 8th generation is considered "true blood", to the best of my knowledge there is no "pure blood" in ameraucanas.
if your breeding EE's its a true muddy line. most breeders of EE's breed toward blue egg color, or breed for variety of egg color. keeping track of the offspring's egg colors sort out 2 year old roosters for traits you desire. if you decide to breed an EE for color, its best to match the qualities you want in both the hen and rooster. cull offspring aggressively and line breed.
araucanas to the best of my knowledge there are no true araucanas in the US. I could be wrong I have been wrong before. If by chance you do have true "pure blood" araucanas you would have to breed to pure araucanas to keep the line "pure blood". if its a crossed line, and I think they are - it doesn't hurt to out breed and breed back for purity. but, you will never have "pure blood"
both "pure blood" and "true blood" are showable and when bread correctly would be nearly impossible to tell apart without looking at dna. if I did have a "pure blood" line I would not cross it up unless I just had to. for instance, when I get the brussbars - I will breed 3 lines from them. there will be the "pure blood" line developed in the UK, then there will be a recreated line developed in Canada using a wrong, but very similar Sussex. (at least this is what ive been told by a Sussex breeder, still learning about that breed too) I will also do a cross between highly selected roosters in the Canadian line with a couple pullets from the UK line for some genetic diversity.
I hope this helps.