Variety is the spice of life. I love steak, but if I ate it three times a day, day in and day out, pretty soon I would be craving anything else...even Spam!
Different bugs will give your frogs different things to hunt for, different favorites, and, as Frogparty mentioned, more of a chance for a couple of them to get well established in.
Luecs are a great choice for a first frog, and while they are a good group frog, your viv is a little small. Don't try to stick too many in there. Preferable just a pair.
When I asked about thumbnails earlier, I misread the title, I thought it said 10 gal vert.