Khon Kaen is a great city, but it's a new city and a lot of people on vacation travelling about want to see old ruins or architecture or other historical sights, and Khon Kaen isn't that sort of place. If they aren't looking for that, then they want natural beauty, and it's not that sort of place either. It's a current, modern, Thai city with good nightlife, good food and a large univerisity with a vibrant life around that. My son goes to school here and I love the city when I can get out to it. But it's not on the tourist list.
It sounds like my kind of city. Visit the museums, night markets, a bit of nightlife, walk around enjoying the Thai atmosphere without the big tourist sales pitch and move on when we feel like it. I hear they have horse racing as well so would like to check that out as well. If it's anything like Ubon I think I'll enjoy it. Looks a bit bigger but not too large.
I'd say about the size of Chiang Mai, but NOT with the history and a smaller expat community. I like it much more than Ubon. Has a nicer feel in my opinion. Has several good night markets with those gyros like sandwidches that are great (if not very Thai). Has some good nightlife too. The Pullman is a great deal for the money, but it is a bit pricey.