I just got my FugeRay 16" and I've got to say that even from a simply aesthetic point of view, the brighter light really makes the tank pop.
Side by side, the stock lighting simply doesn't do it justice. I also think that the amount of light the FugeRay 16" produces is just enough that you could avoid CO2 if you chose, but also enough such that CO2 and ferts could significantly enhance plant growth.
This also means that the Ray II 16" or 18" will bring you into the medium-high light range.
I personally think that the $45-$50 in upgrading to the FugeRay 16" is worthwhile.
I have a 20G that is by all standards under-lit for its 18" depth (light sits at nearly 2ft above substrate!). Plants grow but they tend to be stringy, and tall and "messy" which met my aim for a low maintenance, natural growth look in a tall tank (wanted to fill out the higher levels of the tank).
For a 10" tank, however, that is not the growth I want. Tall, stringy plants in a short, rectangular tank is not my idea of visually pleasing. If you would tend to agree and want compact growth, then I think the lighting upgrade is necessary.