I do take toys out of circulation from time to time. Either they haven't been played with in a long time or I get sick of the dcks not picking them up/fighting over them.
I always find lots of unique things over the summer at yard sales and add those immediately. If they're a hit, they stay. If not, they get donated in the fall. I have a lot of basic stuff but for some reason, the kiddos don't use their imagination to expand their selection of toys to play with. I have a nice set of wooden blocks, with different sets of accessories but they'll always choose the plastic dollhouse and Little People. I have a mirror in my play kitchen area and instead of playing with the actual kitchen area, my twins will sit there as long as I let them, to make faces and gawk at themselves.
I know as soon as the twins leave in a few more weeks, I'm switching my playroom around for the summer.