One way to deal with a speed run is to embrace it! Stay confident in your ability to ride along! As Peter said, try to anticipate and know when and why you'll get overpowered and take preemptive measures to prevent that. Riding closer upwind, and deeper downwind helps.
As per the touchdowns, I have quite a buoyant board, and I love the sound it makes when just skimming the crests of the chop, and it's a bit of a game to play with the surface at times as opposed to always stay 20cm above it. Provided I'm not borderline in terms of power and can afford that. Even when carving tight S, touching down on some parts of the carve is fun and give some sort of extra bounce. Anyway, a touch down friendly board can be fun, and I can see that it would be possible to add tons of drag to slow down. Although reaching for the touchdown to regain control out of a excess speed situation comes with some risks! Best to use that to not accelerate in the first place.
One day I've had a 2m string of kelp caught on the top of my mast, and I rode that for a few tacks until the next fall, it was adding some drag at the back, yet, not affecting the flow and lift of the foil as such, unlike when there's a bit of seaweed caught on the wings or fuse. So I had a stable foiling platform but with some drag, and I thought that having a 2m rope, or a non attached leash dangling at the rear could be a good way for a beginner to build confidence.