Linked bouldering circuits, what are the secrets?

I'm thinking of switching out some of my treadwall exercises for linked bouldering circuits, but don't have any experience with them.

Seems like the variables are-
difficulty of uproute
difficulty of downroute
rest time if any
number of reps (ie overall duration)
and finally rest (on the ground) between sets.

Would anyone be kind enough to share their experience?

I would like to be more able to pull hard when somewhat fatigued, and also to recover better while still on the wall. 

Well, what are your goals? Endurance training gains are short lived enough that it’s got to be as close to simulating as possible. 
Unless you’re aiming for 40+ moves, I wouldn’t make the downclimbs super hard, it would be silly to fall on the downclimb. 
Look at Climbstrong free energy system articles to see what you want to progress regarding rest lengths, link lengths, increasing volume, difficulty etc.  Each variable changes things in different ways. 

I’m guessing you’re climbing in CCC/Boulder area is bouldery/cruxy to rests of different sizes, is that correct?

Jon Rhoderick wrote: Endurance training gains are short lived enough that it’s got to be as close to simulating as possible.

I’m guessing you’re climbing in CCC/Boulder area is bouldery/cruxy to rests of different sizes, is that correct?

Good guess, although there are some Flatiron routes I mean to try that are more continuous. Still they usually have some rests.

Funny though, I usually find aerobic power/capacity gains reasonably persistent.
Stamina doesn't last that long for me, maybe a couple of months.
Power on the other hand, just slips away.

In your situation I’d set a V5 a V4, climb the 5, downclimb something in the V2 range, get to a poor rest at the bottom, shake for a preset time, then up the 4, and then modulate difficulty / rest periods as you see fit.