There really is only one good prospect being traded and that is Foscue and Leiter shouldn't be considered a good prospect anymore. He is looking more and more like a AAAA pitcher than anything else right now. He may have to become a reliever where he loses a lot of value as I am not sure you could count on him being consistent enough to be a late inning reliever. He still has some time left but he shouldn't be considered a good or a really good prospect anymore.
The Brewers side is extremely short on value even with Semien's contract. I think the Rangers would rather pay some of Semien's contract than throw in prospects. It is a moot point anyways as I don't believe the Brewers would take on much of Semien's contract anyways. It is just way too much to take on for a 30+ 2B even if he would average 4-5 WAR a year over the span of his remaining contract. It would be better to just sign Adames as he should get about the same per year as what Semien would be making though for about 2-3 years more.