Good points here. I am cynical about fads and about zealots. I also have a surf-first attitude. But I can report that foiling is a nice addition to the quiver. It isn't "the answer!!!" or "going to change everything!!!", but it's a new challenge that can make those "meh" days fun again.
I took kite lessons in France on a family vacation in 2010 and saw a guy out on a foil. At that time, the only foiling in media was the Laird tow-in show. I thought it looked pretty wild, but figured it was out of reach. When I got home, someone had posted an ad for that same original carafino, for "cheap" (relative to the crazy $ new). A very rare fluke ... so I grabbed it, even before I could kite. It sat in the corner for 2 years, while in the meantime foiling took off in the kite racing world, then hit the mainstream.
Anyways, point is, that early carafino foil was a modified AirChair they use for waterskiing. Designed to ride at about a 30 degree angle like a water ski, tons of drag, very slow, easy to get up but low top end. Fun novelty to be up above the water, but that's about as far as it went. No one would call that a game changer. But I upgraded to a stringy foil (similar to zeeko black/white or carver wing) and it's insane how different it is. Like a knife through butter, no resistance in the water, turns crazy fast, and holds as much speed as I realistically want. This is different enough, and offers enough new capabilities, that you could spend a whole bunch of time and still have stuff to learn.
I am finding my main foil interest is carving swells downwind, it's a super cool feeling. I want to carve tacks like Greg Drexler ... though the gymnastics elude me. On any given day, I have foil, twintip, and surfboard on the beach, and ideally use all 3, mix it up, keep it fun. But if there's breaking waves, no question, I'll be on my surfboard.
Bottom line, if you have a few extra $ sitting around, definitely a fun new toy. Or review the DIY threads for cheap options!
PS
Boards: I agree, most of the focus on boards is nonsense. People are using wakeskates, skimboards, and surfboards, makes little difference for non-racers.
Roller: foilers are NOT the rollerblades of kiting, that is twintippers, especially in boots! Foilers are the unicyclists of kiting. Complete with red clown nose and horn.