Physically, keeping your workouts new and dynamic forces your body to adapt to more variable stimulus and keeps overloading the body in new and challenging ways. Mentally I have definitely avoided burnout by keeping things new.
As the spring season is upon us, training anaerobic endurance is a great way to transform that strength and power gained bouldering during the winter into route climbing fitness!
Here are some exercises to try out that are outside the usual 4X4 circuit:
Select around 5 problems (has to be an odd number) in ascending difficulty. The 5th problem should be somewhere near your limit but should be a problem you have sent. Complete the 5 problems and then repeat them in reverse. Example V4,V4+,V5,V6,V7,V6,V5,V4+,V4
Repeat this pyramid at least 3 times resting between each set for the same length of time it took you to complete it.
Traverse into Problems:
Most routes have one or two main cruxes to be dealt with and a bunch of other climbing in between of variable difficulty. This exercise is an excellent way of simulating a route climbing experience without having to rope up. Select a problem at or slightly under your limit (This may take some experimenting to find out what you can do). Using existing holds in the bouldering area at your gym, pick out a traverse (30+ moves) which ends at the starting holds of your problem. Climb the traverse into the problem building in at least one rest hold prior to the "crux" boulder problem. This exercise is really fun and simulates route climbing as best as you can get without a rope!
30 Problems in an Hour
This exercise is a great stamina exercise and depending on how many problems you do (can be any number. Doesn't have to be 30) can be absolutely devastating! Pick a grade range such as V3-V7 and do as many problems within that range as possible over the course of an hour. Repeating problems is allowed. Give yourself points for each problem completed based on the difficulty of the problem. This keeps you honest and can be fun if you're doing this with a partner.