To think about equipment is normal. If you have a Nikon and a RZ you already are equipped to take quality photos. I beleive that the first priority is to consider the end usage of the equipment. What interests you and what are you trying to accomplish are the first questions to ask yourself. Then what necessary equipment is properly suited to accomplish that end is the next question to be asked as well as how you like to approach your work.
If you want 8x10 photo of children being themselves than a good rangefinder camera is very suited to that task. If you are interested in sports photography then your Nikon may be much more suitable. If you are taking formal portraits and have 16x20 prints as your upper print size then a Mamiya RZ can hardly be be beat in roll film.
Once you have made such decisions then expand that system. For example a Nikon with 5 good lenses that is well to a photographic application will be a better choice than 5 cameras each with only a normal lens.
Make sure you have good quality darkroom equipment and lust after good print quality not more cameras. Do your work. Do your work. Do your work.