Possibly the 47's can be reduced a little, or a turn or two removed from the primary winding (that drives a transformer, right?), but that most likely overdrives the heater, leading to even shorter life. VFD fade is usually due to phosphor wear, unavoidable. (Come to think of it, I wonder what temperature it could be annealed at. Probably nothing you could do without an inert-atmosphere oven though, or melting the glass envelope for that matter.) If it's due to fading cathode emission, raising cathode temperature will work momentarily. Increased plate voltage may not be possible, due to other limits (driver voltage rating, grid cutoff voltage shift).
Tim