In the standard game, no they're not worth it. I never research beyond level 3 in the standard config. But... in my custom config I've removed the 'enhancers' and put a more logical type of facility in levels 3-6 of each resource. Value improvement plants, a seperate one for each resource! Renamed to something that sounds pseudo-technically capable of doing what it's doing, of course. Yes, I removed the "all three resources" improvement plant in the planetary improvement techs and left just the atmosphere facilities. How logical is it that ONE process/machine can improve all three resources on a planet? Not at all! So, now it's more logical. This way you can have to specially research the type that you need. Now I'll have to go edit all 20 of the AI research files to deal with this.
Oh, well.