I guess it all depends on two things. One, how much a glossy cover matters to you. And two, how many games you need covers for.
See I have roughly a little over 400 games to case between my NES, SNES and N64 games so going with glossy prints would get quite expensive very fast and therefore would probably take me twice as long and twice as much to case up all my games. So instead I went with legal presentation paper (500 sheets for 20$) which is thicker than standard paper and should cover me for all my covers. Much cheaper and the quality of my covers are still of very nice quality.
But if your only printing out covers for say 20-50 games than sure, why not go with the Semi-Gloss.