The logic of a lighter bike being an easier ride is, I suppose, unassailable. But there is great merit in adapting what you have for the time being, to ensure that this is really what you want to do, and to help you determine what characteristics your "ideal" bike needs. It's not just about weight. On a long ride position becomes very important. Are you likely to be a "fair weather" participant, or round-the-year - mudguard clearance, even if not fitted all the time, might be important (and yes, RaceBlades and clip-ons work, but they are not as effective as proper guards).
I keep saying I'll get myself a lighter bike (than my steel Roberts, which weighs a ton compared to many of the steeds I see on audaxes), but what I have is comfortable, and generally reliable. And I suppose keeps me stronger, as I have to push so much more up the hills. But then my own 92kg is a poor starting point!