The first linked site appears to concern itself wholly with halogen bulbs. It claims of low-voltage halogen bulbs that, "They also produce a nicer light, with warmer, brighter and more vibrant colors."
The second site's entire argument for low-voltage light being better seems to rest entirely on how configurable and remote-controllable low-voltage lights are, as well as how much easier it is to scatter gobs of them about to achieve your lighting plans for world domination.
I am inclined not to trust the first site, because their argument doesn't make intuitive sense and they provide no citations to back it up. The second site's argument makes sense on its face.
I can't speak to halogen bulbs, but when it comes to LEDs, I would not expect any difference in light quality between a line-voltage and low-voltage LED.
I don't know of any LED bulbs that actually drive the LEDs at line voltage. The ones that you can just screw into a line voltage socket just include their own DC rectifier, the same way that CFL bulbs include their own ballast to drive the fluorescence.
I would expect you can get finer control by putting your own transformer in front of a line of low-voltage LEDs, and your resulting lighting system will probably be more efficient and flexible. (As an example, I know an LED retrofit lamp I recently installed could dim down to only 5%, whereas you might be able to dim the LEDs throughout their full range using your own transformer.)
You're not missing anything. LEDs that have a high CRI is a relatively new market segment, so the selection is limited, and prices are high. LEDs use the same tricks as fluorescents to reach reasonable CRI levels-- multiple phosphors with different spectra excited by the lamp's primary EM emission. So the potential exists to equal or exceed the best fluorescents. Right now, the consumer LED market is focused on replacing lamps in non critical applications, and thus tend to be rather low color temperature and only modest CRI levels. This situation should improve in the future.
"High" CRI fluorescent tubes are available in color temperatures from 3000 to 6500K, with CRIs between 80 and 90, and at reasonable prices. Right now, this is probably still a good solution for many applications. If the performance of these lamps are not adequate, halogen lamps are the only reasonable alternative. LEDs are not quite there yet.
Best Answer
Back when every lamp was an incandescent bulb, things were simple. Then Mr. Tesla came along... In this day and age, you can't just slapdash random hardware together and expect it to work together.
The dimmer is not listed to drive a DC power supply, is therefore not legal to use with it, and in any case, is unlikely to play nice.
Some DC power supplies are multi-voltage. Dimming is completely ineffective on them, they see dimming as lower voltage, and draw more current to compensate, potentially overloading the dimmer.
If you want to go Low voltage lighting, you will need to get a power supply compatible with whatever LEDs you expect to use in the future, and then get a dimmer designed to dim those LEDs and halogens.