It's possible that your perennial geraniums need dividing or thinning. Some types spread quite quickly while others remain in a tight clump for many years. If they appear to be growing in a thick mass, you can simply dig out sections to transplant elsewhere (or discard if you have no place to plant them). The remaining plants can then fill in the bare spaces, and with less competition may indeed bloom more profusely. If you haven't fertilized in quite a while it would be helpful to do so. Make sure that you use a fertilizer for blooming plants (one in which the first number[nitrogen] is relatively low). Too much nitrogen forces leafy growth at the expense of blooms.