Getting a complimentary upgrade for 5-6 nights would likely be a stretch, so if you want the space, I'd use the TSU. The suite I typically get is a full one-bedroom, but they do not have a pull-out sofa. So you may need a roll-away. Sadly, the Galleria hotel has no desks in the rooms. The have a low table that can serve the function, but I prefer a desk. The rooms coordinator and the GM told me they would get one in my room for future visits if desired, so you can ask for one if that is important to you.

The Galleria lounge is a pretty typical lounge in terms of food. Breakfast will likely be scrambled eggs and a hot breakfast meat (bacon or ham), with standard pastries, cereals, fruits, yogurt, smoked salmon. Then they put out nuts/chips/giant cookies through the day before doing a hot dish (which can be an appetizer or more substantial), veggies, and dessert for the evening.

It sounds like you are going to be out and about, and I don't think you would go wrong with either hotel, but I personally would do the Galleria. In addition to the ice rink, there is a kids play area with a "mini-Galleria" for kids to climb and jump around on. My 5 and 7 year olds are typically good for 45-60 minutes running around and playing chase on it before wanting to do something else.

Cayann is correct about the Aquarium restaurant and Discovery Green downtown. The Aquarium restaurant is touristy and overpriced, but my kids love it (there is also a ferris wheel). My kids love the Children's Museum, and I can geek out in there with some of the science things myself. The children's museum and the zoo are in the same area, but my kids would be too tired to do both in the same day with all the walking at the zoo.

Houston is great for food, and you shouldn't have any difficulty finding whatever you think you would like. I believe you are contractually obligated to get Tex-Mex while visiting Houston, but you'll find great restaurants in every genre of food. If feeling adventurous, Houston also has the second larges "Chinatown" (although almost all Asian cultures are represented) in the country. So you can get authentic Asian food as well as American-ized versions.

Galveston will be a day trip from either downtown or Galleria (solid 60-90 minute drive each way from parking to parking). The water will be too cold in March for swimming (unless you are extremely hardy).

For me, I wouldn't consider Dallas a day-trip unless you are flying. I hate driving, and it will be a four-hour drive each way. Unless you have a specific reason to go to Dallas, I'd do Austin or San Antonio instead. They would still be big drives for a day trip, but shorter (and more interesting) than Dallas. I'd grab a cheap Hyatt Place for an overnight in either place while keeping my suite in Houston, but again, I hate driving so that may not be a big deal for you.