The real issue here is not the bike IMO.
I didnt buy the 690 when I had the chance, I went for the 610 instead, for various reasons. But that was when we had two bikes of that type available - now there is only one, unless you buy second hand.
The real issue to me is actually social dynamics - strange as that may sound.
The simple fact is that the type of riding that a 690 is good for is very different to what most people do. So if your mates all ride 990's or even worse, 1200's etc, then its going to be difficult to ride a 690 with them.
You wont be able to cruise at high speeds with them on tar - especially if they push it.
Depending on how much skill they have, they might not be able to keep up with you in technical terrain. And even if they have the skill, they just may tend to avoid the technical stuff because its a bit harder on a big bike. So you are going to be constantly wanting to do different types of riding.
So unless you ride alone often, or are lucky enough to find mates that also share your taste in terrain and type of riding, its going to be difficult to own a 690, and the pressure is always going to be there to get a bigger bike simply because more people go that route.
Personally I think the 690 class of bike is exactly right - for my preferred type of riding. There are a few things I would want to be different on a 690 specifically, but that's just details.
To me, all the other bikes (including the other 650 adventure bikes) are just too road orientated. I want something that's derived from a racing enduro bike so that it handles well like a proper off road bike, but I do need to ride on roads - so it must be able to cruise at highway speeds for longish distances.
The 690 is the only bike sold currently that fits that description. As I said, I just wish there were more choices in this class.