Most of the low end controllers can control two valves at once. The higher end controllers can do 4 or more valves. If you are going to remove valves to decrease the number of zones think carefully about how you combine the zones. Sprinkler head types, amount of sun, and soil type all have an effect on how much water an area needs and once you remove a valve and physically combine two zones you will lose your ability to water those two sections differently.
There are timers available that can run two or more irrigation programs simultaneously so you can take advantage of your increased GPM output from the lake and still keep all your zones.
Also, if you are using rotors you can look into increasing the nozzle size in each rotor so you can water each area faster. Obviously you don't want run off, but many times low GPM systems and using nozzle sizes that are smaller than they should be leading in uneven watering due to wind drift and improper matching between half circle and full circle rotors. Now that you have more GPM to work with this is also something you should look at.