Throw the WPG rule out whether you have live plants or not being as it has no place anymore in the hobby with the advent of HO lighting etc. The WPG rule was basses off of either T12 or T8 lighting(I don't remember which) and all of the other lighting methods(T5, compact flouresant, MH, LED) all have higher PAR values and lumen output per watt...
Without plants, just worry about what looks good and not wattage. If you plan on going saltwater later, buy that fixture when the time comes, who knows, the fixture you like now, that you would spend $800-$1200, might be $200 in the future, because it is likely to be "old news".
Shop lights are ugly, but take the time and buy some wood to make a nice looking floating canopy to hide some shop lights in. They are cheap($17 after tax for fixture and daylight spectrum bulbs, around here anyways) and use as many as it takes to make it look right to you...
If not, keep using your current setup. Trust me, more light is gonna kill you in algae problems if there are no plants to use up nutrients...
Trust me again, I have bought some expensive fixture because I thought they would look better, but without plants I just got algae. Now I run quality T8 shoplights on a lot of my FW tanks that have no plants, and the fish look just as good as if they were the expensive ones...