Let's face it - the Mario cartoons were absolute crap with little real artistic effort put into them, at least in terms of story and the cartoon art.
Regarding old versus new - I believe that owners of characters sometimes feel the need to update them to appeal to differing audiences, usually wider ones, and sometimes alienate "old fans" by making such changes. Yoshi is a victim of this. In my opinion, the greatest character conception of Yoshi occured when Nintendo Power issued it's Mario World comic in the early '90s. Here's a link to a page containing the comics.