should i upgrade ?

ive recently been playing alot more of my old records. i have a denon dp-45f and a cambridge audio 540 preamp, playing through about a $3500 amp & speakers. most of my records are in vg+ condition, but i notice while most sound only fair through this set up some, say 1 in 5 sound great i mean 20 to 30% better. this has me wondering since my record collection is what it is, and i only buy used records when i add to it. would a better set-up bring the fair sounding records up to great? or since this system seems to play some records very well that its probably more my records than my system ? thanks for reading.