You're on the right track but - assuming the slides themselves aren't too bad - I think you should be able to much better results than those.
I copied several thousand slides from a collection that spanned some 20 years, using a fairly simple Nikon digicam, and none were that disappointing!
For example:
http://www.pbase.com/isolaverde/image/97539277http://www.pbase.com/isolaverde/image/107258542For background, method and more examples, see here:
http://www.pbase.com/isolaverde/slidecopyAnd, at the risk of repeating some of what's there, can I offer a few more thoughts and suggestions?
If you can attach the slideholding device to the camera, the scope for blur-forming movement can be almost completely elimated - which then allows you to use the longer shutter speeds that come with lower ISOs, which should improve the overall image quality significantly (and try to arrange a level of lighting that allows you to use optimal shuttertime/aperture/ISO combinations).
White balance. I've found it much better to illuminate the slide with daylight. Most of mine - and yours too, I'll bet - were shot on ordinary daylight-balanced film stock and almost all other light source is likely to lack some of the wavelengths and colours that were recorded by the original - without those the camera's going to be hard put to give a decent copy!
If using daylight or flash, select the most appropriate of the camera's WB settings rather than Auto White Balance, so the camera's WB choice isn't influenced by the colouration of the individual slides.
As far as is possible, be sure to distance the reflecting/illuminating source from the camera sufficiently that any surface detail it may have is well out of focus (beware of artex ceilings for instance!).
Try different camera/slide separations and zoom settings. Clearly the one you've chosen isn't giving very good results, and I'd guess that it's because the slide and camera are too close to one another - causing the edges of the image to be so out of focus and distorted.
Reviews say that it's possible to use Macro throughout the Optio 30's zoom range, so instead of using the extreme wide end of the zoom range, try backing off a bit and then zooming in until you fill the frame with your chosen part of the slide (but don't expect quite the same quality of results if you crop in to too small an area of the original!). You should see a difference!
Slides have a huge brightness range and, with shots like the water wheel, you may find that you get a better result if you turn the camera's contrast down to a lower setting - if there was any shadow detail to start with. Also, it may help to use the shooting histogram to check when exposure compensation is needed for very thin or dense slides. You'll soon come to recognise those that require some intervention. For example, although I've done my best to improve this one, a better starting image would probably be the answer!
http://www.pbase.com/isolaverde/image/108063993And be sure you focus correctly. I use a little program called PhotoME, which is showing that no focusing point was active in the 'Gardens' image for instance.
Hope some of that's useful,
Peter