If you are not interested in a registered herd, would you not be money and time ahead to purchase one very good registered maternal bull and put him on your current cows?  Or AI your current cows to a couple very good, proven, high accuracy maternal bulls?  Keep all of your heifer calves and do it again. When you get a very good cow that is what you are looking for and she has a bull calf, use him as a bull.

True you are only improving half of the genetics at a time but at least you know what you've got and you are not "putting all of your eggs in one basket" as Pony Express puts it above.

Maybe buy a couple very good but older cows to add to the mix. Get a calf or two out of them to build on.

I think the initial key decision here is are you going to AI or use a bull. Even if you go with embryo transfer what is your plan for next year?

Even with embryo transfer, the calf hits the ground in spring 2015. Assuming 50% are heifers, they are bred in 2016, calve in 2017....

Any way you look at it improving or growing a herd of good cows is a S L O W process.

Jim