Hey Rick, I'm good. Been a long time.
I would say a good A, especially a Marstrom, is the opposite of fragile. I'm sailing the odd-ball Bimare 2-up (it's designed for that). The main thing I notice with it is that the puddles of resin are missing from the hull. It has a pretty normally sturdy fiberglass construction, just done nicely instead of being glommed in with excess resin. I've seen Marstrom Tornadoes and the Marstrom M-20 and they are some of the sturdiest, best built, most nicely laid-up boats I have ever seen. Yeah they don't have some of the thickness of resin and gelcoat on the bottom that the Hobie 16 has, but they are certainly "sturdy". I think you'll find the boat nice enough and light enough that you won't want to drag it around the beach.
Now Bill is mostly right about the single hander being designed differently than a double hander. I'm assuming that you won't add a second trap, and that if Karen's going out it will be for a fun sail, not for some hairy white-knuckle ride in big surf and big winds where you're pushing a hull under every other wave.
If you sail it the way that it sounds like you plan to then I think the Marstrom A might be that boat to last you the rest of your life.
2 other minor things to look at.
1, look at the age of the guys sailing A class catamarans. You'd be a youngster by comparison to many. Yet the boats go fast as hell around a triangle.
2, talk to Mike and Carol Fahle. To hear Mike talk about it the used A he bought has been pretty close to a religious experience for him. And I know he has taken Carol out on the boat with him also, so he has tried some of what you are talking about. Now he's not as big as you but Carol is bigger than Karen and his A is a Boyer not a Marstrom. Everything I have read leads me to believe the Marstrom is the right A for big boys.