That's something to worry a little about...but I think Coors home/away splits get overstated for a few reasons:
1. Outside of Coors, the NL West is a hard place to hit. Three of the other four parks are pitcher's parks (Petco, AT&T Park, Dodger Stadium). About one third of Fowler's career road ABs have come in those three parks. He has an OPS of about .630 in those three places, compared to about .725 in all other road parks. If the Cubs traded for him, he'd pick up a high proportion of his road PAs in two parks that are good for hitters (Miller & Great American) and two that I perceive as fairly neutral (Busch and PNC).
2. Most hitters are a little better at home than on the road.
3. I don't have any proof for this, but I imagine that Coors is such an outlier as a hitter's park that it results in a kind of "hangover" effect when the Rockies go on the road. Many Rockies hitters likely have pretty different approaches at home than they do on the road because it is so much easier to hit. But in a more neutral park, they probably wouldn't make the same adjustments.