I have a 46 bow with 96 watts, and for over a year I have been running it on weekly Excel + light EI dosing. I have been able to all but a few medium light plants.
Personally I would replace the bulb because it really opens up your plant options, and still is low enough light that you don't need CO2
or dosing ferts every day. With the 50/50 bulb you will be really limiting your options, with the full 96w bulb there is not that much more maintenance required. I think it comes down to how much attention you want to give to the tank and how much reading you want to do.