I'd be curious as to how you (or anyone else) like the klr coming from a tw. I don't plan on getting rid of my tw, but have considered getting a larger dual sport/adventure bike for longer trips. I'm just not sure how much off road capability I would be giving up. The 400+ lbs most of these bikes weigh scares me too
Weight is a concern. Try 500+ pounds with fluids and luggage. The center of mass is several inches taller than the TW, so it is also noticably more difficult to keep up in slow going on low traction surfaces, as well as more difficult to pick up when it falls. I've seen KLRs and F650s and such do some fairly nasty terrain in exceptionally skilled hands, but it wasn't easy on the riders. Those riders spend 50+hours per month actually riding dirt trails and such, and have been doing so for 40-50 years. Lesson to learn is that such bikes are extremely capable in skilled hands, with the key being "in skilled hands." I've seen others who consider themselves as having "skilled hands" suffer a series of crashes, damage, and injuries on the same models of motorcycles on far less difficult terrain. Carefully consider your skill level before taking your KLR offroad. Are you physically able to handle such a top-heavy motorcycle?
The KLR is an excellent adventure bike. It is capable of shattering any speed limit in North America, is fairly comfortable on the highway, handles twisty roads quite well up to the limits of its barely adequate tire sizes, ..., in fact, KLRs handle any road quite well. Road surface, grade, condition, and weather pretty much don't matter, as long as it's a road. The 2008 redesign significantly improved highway performance without compromising secondary road performance, though crash survivability is significantly reduced. It's load capacity allows for ~330 pounds of rider and gear, but tire life suffers due to high loading.
I do intend to add another KLR to the stable eventually. It will serve in the adventure roll when the trip requires quickly eating up miles on the highway. I'll only discuss the functional mods here that address the bike's shortcomings, leaving the personal preference gadgets and comfort stuff to, well, your personal preferences and comfort needs. KLRs have more farkles available than any other motorcycle on the planet, so anything on the bike can be improved. You have been warned.
First up is crash protection. It doesn't take much of a drop to render a KLR unridable. Case, fairing, and hand guards are mandatory. A significant luggage rack with pannier brackets will suffice on the aft end. Avoid adding a centerstand--the mounting system can sheer the footpeg bolts when the stand grounds while riding.
Next mods for any KLR should be doo-hickey and subframe bolts. Most riders in the North American market will enjoy the same performance the rest of the world gets by rejetting the carb. You could go out and spend a bunch of money on a "jet kit", or you could just use Kawasaki parts and enjoy virtually the same performance. Pretty simple formula, actually. Same as a TW. Up 2 sizes on the main, washer under the needle, 1 more full turn open on the pilot screw, call it good. Not perfect, but entirely satisfying to 99% of riders, and a much better starting point for finer tuning than stock.
Improve traction and load carrying capacity by changing rims and tires. 150/70-18 on a 10-13mm wider rim on the rear allows several choices of well-proven tires--Trail Attack, TKC 80, Karoo, Big Block, and MT 90. Match with a 120/90-19 front on a 2.125-inch rim (bazillions of tire choices available) to solve the barely adequate tire problem. You'll enjoy superior traction in all conditions as well as significantly longer tire life.
The early brakes suck. The second generation brakes don't suck quite so bad. Neither are particularly confidence-building, especially when bigger wheels and tires are added. That said, I find even the early brakes satisfactory for my riding style, which emphasizes extreme situational awareness that allows smooth and gentle control inputs through thinking far enough ahead to allow deceleration with engine compression only and preservation of momentum. Tdub's rear brakes are original, with about half the lining left, at 48,xxx miles. She is on her 2nd set of front pads on her street wheel, which has probably 35,xxx miles on it. I realize most riders do not possess the same traffic sense as I've developed with somewhere north of 3 million miles driving and closing on 700,000 miles on 2 wheels, and that others are far more susceptible to needing better brakes. 1st generation bikes really need a better front rotor and pads on both ends, while 2nd generation KLRs can get by with just upgraded pads. I've heard good things about stainless brake hoses, but the only KLR I ever rode with them was a 1st generation that was spoiled rotten (pads and rotors on both wheels) and its brakes were excellent.
The 1st generation suspension isn't much different than a TW's. Emulators, springs, fork brace, and a shock can make a world of difference. The 2nd generation suspension has a couple inches less travel, but it is much better controlled in stock form. Still, there is room for improvement.
After that, it's all personal preference.