Vaughn, as well as many of these other Brewer players, will play fine with the Brewers right now. But when they leave, they'll drop back down. There's something about what they do that gets performance from players, sometimes just for the short term, or just in a certain role which is all they need at the time.
At the end of the day, the Brewers are just really good at what they do. The get excellent value, turn it into performance on the field, then keep refreshing with the same model each year, so they rarely wind up having to pay top dollar.
Also notice, they don't go hog wild at the deadline either. Look at teams like the Padres, who everyone was saying did great at the deadline. The Brewers are on the cusp of the LCS and didn't spend key prospects to get there.