Ken's website looks pretty useful. I'll start reading some of that. I have Lightroom and have played around with changing the WB settings. The issue I always seem to face is more of a lack of clarity and sharpness in the image than anything else. I think a lot of that comes from the limitations of the D90 (being less than full frame) and the fact that I'm normally maxing out the lens when I shoot. And the fact that I'm a hack.
Poor quality in an image is almost always a limitation of the lens, not the camera. Now, your D90 won't compare to what a D3s shoots, but if you put a pro level lens (f2.8 Nikkor) on your D90, and really dial in your settings, you'll get high quality images. The limitation will come in low light/poor light conditions. That's where the dollars spent in a body start paying off. I can show you pictures shot from a D3100 with my 70-200 f2.8 VRII vs the shots coming from his 18-105, and it's not even close. The 70-200 is just a far better lens. As it should be. Invest in glass first, and always. Than invest in a new body.
As far as the DX FX argument goes, it's a nonsense argument. I shoot with a D300. True. DX. Pro-sumer camera. I'll take my D300 and put it against the D800 that just came out, and kick its ass all over the airport, or anyplace outside of a studio. Why? My 300 is a better camera for the mission. With a battery pack on my 300, I get 9-10 FPS, and can simply take more images than a D800. I play odds. If I shoot 500 images, I'll get 50-75 useable ones. Put the D800 in my hands, and I'll take 300 images. I may get 50 workable images, if I'm lucky. It's not a knock on the 800. The 300 is simply a better tool for the job. I've used the D300 since 2009. I started with a D70. There are images on this forum that were shot with the D70 (the Goshawk pics, the B-1 refueling pics, and T-bird pics). Everything you see with a 2009 and later date is out of a D300.
Even today, Ken raves about the D90. I'd shoot a D90 from what I've read about it. I'm convinced that what you're experiencing is from the settings in the camera. I'd take it into a local camera store WITH COMPETENT PEOPLE and have them go through your settings.
Being a hack is part of the process. We all started as hacks. Some of us have natural talent with a camera, but no talent the post-processing processes. That was me. I couldn't post process anything. Conversely, some can create magic with a mouse, but can't tell you how they got the shot they got.