I dont really know whether it is truth or myth but I remember Schmickers saying once that the cheaper ones like SMA and lactogen use a cheaper form of casein protein and that's why they are cheaper, so the more exxie ones are generally better. I wouldn't rely on the probiotics in the formula to boost her immune system as they are not live probiotics, so if that is a concern for you I would be giving her a probiotic added to it when she's a bit older. The gold formulas are richer, and they can be a bit harsher on their little tummys to digest, but that said, many babes are fed the gold and have no problems, it really is a case of finding on that suits your baby the best. By and large though it is a marketing ploy to an extent because they kinda know that you are already feeling a bit guilty for having to use it, so they want to make sure that you *think* that you are making up for that by having formula's packed with OMega 3's DHA's probiotics etc when they are actually better off getting those nutrients from a different source on their own kwim? There is some info on the ibfan website about how they market formula and it's an eye opener. Personally I always used the Nan formula's but back with my first 3, there were none of this gold range, or added goodies so I was a bit jaded about it all from the start as the other stuff all being added seem to coincide with the big trend at the time to boost your own health with Omega 3's and all that stuff kwim? With my youngest one though I had to use Karicare AR as he had reflux and stayed with that brand.

ETA - if you are finding the cost is starting to put a drain on things, check out pharmacydirect as they have it online and it's usually way cheaper than in the supermarkets.