Here's a tip I learned from one of John Gierach's books. If you're thinking about getting a lighter rod, buy the line first and cast that line on your current rod.
For example, say you typically use a 4wt and want to drop down to a 2wt. Buy a 2wt line and cast that line and the flies you want to use with your 4wt rod. You might find that the line does not have the mass to carry your flies. If that's the case, you're only out the price of the line.
Most of the time, I use a 4 or 5wt for gills, and I don't feel "overgunned". It's a personal decision, though. Just get the rod that's best for you.