There are two main reasons people recap electronics. One, regarding electrolytics(specifically), is that they dry out over time(increasing their internal resistance or ESR) or can leak their electrolyte. The other is presentation and that some caps(ie: film/foil) can sound so much more transparent than aluminum and paper. Some prefer the presentation of film and oil caps(different strokes/tastes). Individual components all generate a certain amount of thermal(Johnson–Nyquist) noise and some resistors are noisier than others. Carbon composition resistors are usually considered the noisiest, metal-films pretty quiet and wire-wounds the quietest. One can also tweak the sound of their gear with resistor swaps in certain circuits. ie: Carbon resistors will impart are warmer presentation than metal films, in most circuits. One of the reasons older tube gear has a tendency to maintain a, "warm and tubey" sound(regardless of tubes rolled and chosen) is the proliferation of carbon comp resistors, in those units. I've brought numerous pieces up to today's cleaner/more accurate presentation, with the judicious application of Vishay's metal-film resistors(for instance). Then there were the popular Sprague Black Beauty caps............
