One of the best reasons why Google has turned into such a large company is because it has managed to make good decisions with regards to relevancy. This is seen by the fact that Google search results are exteremely relevent (most of the times). You pretty much find what you are looking for the first 3 times you conduct a search. In contrast, Yahoo and MSN have a wierd way of assigning relevancy and the search results are not that relevant.
Does that mean that Google values themed links more? I personally think it does, because of all the importance it puts into the relevancy factor of its searches.
Think about it, if you have a used car website, and you have other used car websites link to you, it makes you look authoritative and more relevant in the search engines.
Also, research shows that themed links are better than normal links but may be priced way higher than the benefit you get from them.
I have seen themed links from inner pages of websites selling at $4 per link. Mind you, the websites themeselves are only PR 2 or 3.
In my opinion, although themed links are more valuable, you can get other links for cheaper and you can kill the search engine game with quantity over quality. But I did not say get loads of crappy links, because no matter how many of those you have, you will get minimal link juice.
To date, I have only purchased one package of themed links which really hasn`t helped me as much as I thought it would. So I have made it a point to get high PR links from general websites which are cheaper.