Wheels, generally speaking, are regarded as the best upgrade you can make. Having said that, however, whether lighter wheels make a significant difference is a contentious issue. If you start a thread like this, I'm sure you will have all sorts of opinions, with evidence for and against, probably with many an arguement which will eventually devolve into name-calling at some point. So let's not go there...
From my personal experience, with wheels that are *significantly* lighter than my training wheels, yes, I have felt them to handle differently, especially on very steep climbs (of which there are many here in Japan). However, this could also be because lighter wheels tend to have fewer spokes, and so tend to be tensioned quite high, which may make them feel faster.
Rather than lighter wheels, I think you would probably see more results from getting a more aero wheel, unless you live and compete someplace where it is extremely hilly. Also, I have come to the conclusion recently that in many cases, better value can be had by having a wheelset built up custom than buying factory wheels. Factory wheels tend to have things like proprietary spokes, hidden nipples, and very low spoke counts, all of which make serviceability a problem for most of us. Additionally, a good number of factory wheels seem to be lightweight because of weight savings at the hub, rather than the rim. (Whether this is important or not is another issue altogether) So, sorry, no scientific analyses here, and I don't purport to make any, but as one rider's experience, maybe a few things to help you make a decision.
By the way, I see from your username that you are perhaps a Kurosawa fan? 😉 Yojimbo is one of my favorites.