Depends what you want; Progressives and/or heavier oil are the usual bandaid. Actual spring rate should be determined by weight/load and checked with sag. If you ever plan on upgrading from the old damper rod damping set up, then stay away from the progressives 'cause they aren't recommended with the Cogent DDC kit or Race Tech Cartridge Emulators.
If you just want to stiffen up an early Gen2 (don't remember what year you have), you can certainly just swap in the 2014.5+ stock springs which, IIRC, are about 60% stiffer.....there are better options though.
FWIW, here's my KLR suspension post:
Stock KLR suspension is 1980's tech with a damper rod fork and emulsion shock with weak damping and springrates which MAY be marginally acceptable if you weigh 160lb or less and stay on graded gravel roads at worst. 2014.5 NE and up have better spring and damping rates but are the same crappy old design.
The bandaid (cheapy) fixes are;
- many use progressive springs for the forks and heavier oil. This will help with bottoming, wallowing and brake dive but the suspension will be overly harsh and not compliant. Better than stock though. Rather than using heavier oil, I’d recommend trying an increased oil level first which reduces the “air spring” and can stiffen it up a bit without all the harshness of heavier oil…..especially on high speed damping.
- Eaglemike's raising links; these change the geometry and reduce leverage on the shock which raises the effective spring and damping rates. Hopefully you aren't short! Easy and cheap but it's a "one size fits all" deal and it doesn’t deal with the inherent quality issues with the stock shock body and emulsion design.
- a stiffer shock spring. While you likely need a stiffer spring to properly set sag, adding a stiffer spring exacerbates the damping issues and creates an unbalanced (oversprung and underdamped) suspension, particularly as the oil becomes contaminated.
Proper suspension fixes;
- forks: cartridge emulators from Racetech, DDC's from Cogent or Ricor Intiminators all with the proper wt springs. The DDC's are my choice because they work at least as good as the RT emulators AND have the simple install of the Ricor Valves.
- shock; a proper aftermarket decarbon shock. Available from Progressive, Cogent, Ricor, Elka, etc. Again, I think the Cogent shocks offer the best value and use top quality, made in the USA components.
While usage, budget and expectations are different for everyone, spending money on the stock shock is false economy IMO and the more you do, the less sense it makes.....better to spend the money on a decent shock. Many people have done the shock rebuild and spring only to replace it later anyway. I've yet to hear a single regret from anyone upgrading to a good shock.