FWIW, I asked Van's about this way back when. They told me that cracking was an issue many years ago, but they went to thicker skins on the elevators at some point and they suspect that gooping up the trailing edges (with RTV, proseal, whatever) should no longer be necessary. They said the recommendation in the manual is pretty much just a relic from the early days with the thinner skins, but it's still recommended "only as a precaution".
I see only two reasons to not goop it up. 1. The goop may come loose in the future and cause problems. And 2) the added weight (it's not just the weight of the goop itself, but also the corresponding extra weight in the counterbalance arm).
For no particularly good reason I ended up using proseal in one of my elevators and nothing in the other. I'm not flying yet, so nothing to report. I guess we'll see in a few years.