At least it wasn't entirely fruitless.
This will be for about an hour, maybe an hour and a half's worth of play time. I didn't get either of the summons I was going for, but I still got some stuff. Maybe not particularly cool stuff, but stuff all the same.
In another runthrough of Cave Magnes, I got a few bundles of Poison Arrows from the pythons in there, but that's about the only thing of real note. I did learn that if the Mages, which sometimes drop a summon spell, somehow get charmed, they just spam Peep spells on the party, far as I can tell. I don't think I'd managed to get the confusion status on Mages before, but I've been playing this game for 25 years, so it's entirely possible that I have.
After I did the cave a second time, I went back to Damcyan and tried for the Imp summon again for a little while. Even though I didn't get that either, I did start getting more of the common drops from them, which is a good sign. I may get it eventually after all.
There was a moment before I decided to call it a night and post this that I considered just getting the VIP pass in Toroia, just to make this a little more interesting. In that consideration, I eventually remembered that I was getting all these weapons and such cloned up to see if Edge the Ninja could throw them as the game progressed. With that in mind, I figured I'd start moving the plot ahead a little more so I could get on with that and sell the stuff that won't work that way.
So, next time I'm going to go ahead with saving Rosa from Golbez. It'll be awhile yet before we get Edge, but not terribly long if I just get on with it.
Until then, stay safe, have fun, keep gaming, and DFTBA!