How do you figure you actually gain up travel? At best it's an even trade, down travel for up travel. It doesn't let you fit a long body shock any better.
To give an example, say you run a 10" travel shock that's perfectly setup for your up/down range (you use every inch of it) and balanced 50/50, you have 5" up and 5" down travel.
You decide to put on a 12" travel shock that is the wrong range, say it's 1" too long. You now have 4" up travel and 8" down travel, assuming everything else stays the same.
You lost an inch of up travel because the body is an inch longer.
In this example, you could give yourself 50/50 travel again by raising your lift by 2". You'd also need to drop your bump stops down to prevent the shock from over compressing. But any way you figure it, you're actually losing up travel because you will have room the tire could go up, but can't because the shock body is in the way.
The end result is effectively an 80 on stilts, you've really just spaced everything down further. It's actually can be worse, because you've now raised your center of gravity by quite a bit, and gained nothing doing so. By properly setting up your shocks you could see the same gain (longer shocks) with no down side (avoid raising the CoG).
Too often people just drop bump stops and increase lift to compensate for longer shocks (or bigger tires), instead of taking the time to properly set it up.
They've lasted quite a while for me, but I used big beefy ones (not little ones as pictured). You could always use metal ones if the plastic ones don't work for you, or I've heard of hose clamps being used.
