If you've ridden a Honda XR650, you'll have no problem with the KLR's height, which is an issue for some. The Generation2 KLR's (2008 and up) have more breakable plastic. I've never ridden a Gen1 much, but the Gen2's fairings offer a little more protection from the elements and the headlights are greatly improved.
The component(s) (slang term: "doohickey") that adjust the engine's chain-driven counterbalancer are considered by most to be the KLR's "weakest link."
I would steer you here to learn more about the doohickey and other mods and issues that riders have had with the KLR:
Some model years, 2008-2009 are known to burn through amounts of engine oil that most consider excessive. As far as I know, this problem has been corrected. Knowing what I've learned on this forum, I would be hesitant to purchase a used KLR in those model year ranges. Some people take steps to correct the problem, others just keep an eye on their oil level, add oil as needed and keep riding with no problems. Some people with these model years have no problem at all.
Aside from the "styling," I wouldn't consider the KLR a "modern bike." It's fundamental elements and capabilities have remained largely unchanged since it came out in the late 1980's. Nobody foresees any major changes for the future. I would imagine if and when Kawasaki ever stops selling this bike, it will remain pretty much as it is now.
But, I consider that a good thing. KLR's have been around so long that there's a wealth of knowledge about them available on sites like this one. Parts are largely interchangeable and there are tons of aftermarket parts and accessories to tailor the bike to the way you ride it.
It's very dependable and easy for either experienced or shade-tree mechanics to work on and maintain. In the event of a problem, the machine's simplicity and the knowledge of other riders online make troubleshooting much easier. If you have a problem, there's a very good chance not one, but several people have been down that road before and can save you a lot of hassle figuring out what's wrong.
I guess it all depends on what you're going to use it for. I'll compare it to your XR since I also used to ride one of those. The KLR is much nicer to ride on the highway and the water-cooled engine will likely last a lot longer than an XR engine ridden in the same manner. At least for my riding skills, the KLR is just about as capable as the XR off-road, but it's kind of like sitting on a cow instead of a horse. The XR is a very lean and skinny bike while all the plastic in front of your legs on the KLR makes it seem very bloated. With the big gas tank, although a definite plus in my book when it comes to riding range, it will be harder to pick up if you dump it and the handguards and fairings/shrouds around the bank break very easily and are expensive to replace.
I'd been off motorcycles for a few years when I bought the KLR. I already knew I wanted another DS bike and looked at the Honda and Suzuki offerings before choosing the KLR. I use mine for a 60-mile round trip commute as well as lots of gravel road riding and the occasional foray off into the dirt and mud. I'm glad I chose the KLR over the other two because it's worked out to be my favorite. Given my 'druthers, I'd own the KLR and an XR, but I can really only get away with one bike so the KLR it is. There's no way I'd sell the KLR and go back to owning just an XR.