DOS engines can be the most educational, far more than ones with advanced pixel shaders. You can understand them a lot easier, yet they still have world-class optimizations (most of them anyways...).
Think if you were an author and you wrote a book. The library analogy is great, because if your book were to be taken off the shelves because no one's ever checked it out, you would be really, really pissed.
All engines deserve a rightful place in the world. If no one ever stopped to look at the underdogs, the world would be filled with cliches and would be monopolized, which we all know can be devastating to society. You may even find that a small engine has a neat programming trick which no large engine has ever thought of.
Well, that's my opinion, feel free to disagree.