mexican buffet

older folks with little heat....enchiladas chicken with a tomitillas sauce
or buy tomalles from Tropicana in south city. quesadillaswith a fruit salsa. sounds kinda wierd to have potatoes and a couple of salads. How about beans instead? I'd do a green salad with avacado, jicama, tomatoes, pinto beans and a cumin based dressing. top with fried tortilla strips. It's hot here so I'd not serve heavy food if possible. Good luck.

Yeah, potatoes? Do you have access to other roots and tubers, like taro, or yautia, or other tropical ones? While not Mexican, they are similar in that they are starches, very versatile (anything you can do with potatoes, you can do with the other tropical root vegs) -- you can mash, make puffs, make "home-fries" or french fries. I'm currently on a tropical root veg kick, and just adore them.

As for the entrees, I agree that chicken enchiladas work very, very well. Do you have to hold the food in chafers? Would they go for fish? How about a fish dish, Veracruz style? Cubes of any firm, sweet white fish in a tomato/cilantro sauce, served over rice. You can do it for relatively little expense, but it will be delicious and interesting.

Ceviche
bean salad would be dangerous for oldies (no naked flames !)
you dont say if yor in a hot or cold climate so its difficult to make suggestions.

chow

I just catered a mexican theme and served enchiladas. I made them neutral giving the customer the option to add spice if they like.

Served with that was spanish rice, refried beans and all the sides like guacamole, sour cream, etc. Garnished off with diced tomatoes and chive and they loved it.

The enchiladas were stuffed with a mix of pork and turkey meat that was smoked and ground smooth. Mixed with chopped onion, bell pepper, chile powder, cumin, salt and pepper.

Roll up, top with tomato base sauce (enchilada sauce) and cheese and bake.

Sounds good to me
You could do mini sour cream & chive or salsa or both stuffed mini jacket pots. Or crush tacos , chilli cumin & coriander seeds & roll part cooked potatoes & then deep fry & serve with a dip. Flour & eggroll them of course.