There r not much places in houston to visit.
yes if you've already seen other good beaces, its not worth visiting galveston, but still you can have good time riding fairy on galveston, goto galveston water park(it's not big) but for time pass its okay, you can goto kemah broadwalk. Nasa , definitely. Galleria mall, for ice skating and some shopping. There are lots of places for go-karting. Lots of pubs and clubs. Some discos places will be bikini beach and drink houston.
Have fun staying houston.