My first impression is, "if it ain't broke, don't fix it." But it seems you are looking for more.
I think upgrading to a camera with a larger CMOS sensor will give better color and modulation. You will get a lot of other features along with the upgrade, regardless of the model you buy. Your Fuji camera is a 2005 model and there have been a lot of changes since.
If you are using the images for professional publication or printing, I would get the best DSLR I could afford, and include a true macro lens, tripod, remote release, ring and off-camera flash, lighting reflectors and diffusers, and enough spare batteries to do the job. I would be choosing a camera system that offers well-integrated off-camera flash features and macro lenses, a good bright viewfinder, and a fast and large CMOS sensor.
I would investigate adding a true macro lens as they are designed to produce a sharp image across the image at those close distances. Many general-purpose zooms incorporate macro features, but always with design compromises to speed, sharpness throughout the zoom range, color fringing, light falloff and other optical aberrations.
If you are making images for your personal enjoyment, then you can modify that list to suit your budget, weight issues, and satisfaction with the images.
I do appreciate your issues with the batteries, but I think you are painting yourself in a corner. I'm sure the Pentax K-r would provide excellent images, but the AA battery performance isn't stellar, particularly with alkaline batteries. I do like the interchangeable adapter, as it is light and allows using both types of batteries without a lot of fuss.