After 25 years, it seems to be seldom used. If you try carageenan, please send the results to this mail list. I can't find my copy of Merck Index which should have more information. Since I have never seen carageenan mentioned as a gel for microbiology, I assume it does not get thick. Perhaps a restaurant would know a source for food grade agar.
More agar is used for cooking than for microbiological medium.
Pectin makes jelly firm, but I have not tried it for gelling medium.