Maybe something is eluding me, but I just can't seem to make skill challenges work. Maybe it's 20 years of pre 4e D&D influencing my adventure design in a way that isn't compatible with the concept.
I know what you mean. Personally, I love the idea of skill challenges. The problem though is getting them to flow naturally, preserve the roleplay aspect, while also adhering to the "mechanics" of the system, particularly the success/failure.
For me, its a bit of a mixed bag. If I try to keep the flow in character and someone says "What do I know about the crystal?" if I say, well, you'd need to do a nature or arcana check, invariably, everyone at the table will toss a die. So you get a situation where maybe 3 people made their check while the other three missed. Technically, they have now failed the challenge, yet might not have even realized they were in a challenge to begin with.
On the other hand, if I mention that its a SC, then invariably, it ends up "I try Arcana." "I'll try history." "Can I try Diplomacy?" and thus, the flow is completely gone. It might as well be a combat encounter at this point.
The other element I struggle with is in designing challenges that will involve most/all of the party. Information challenges tend to fall to one or two characters, as do social challenges, etc. Physical challenges make the wizard cringe as well. One thing I have found to help overcome all of the above, is to come up with challenges that involve group checks wherein everyone has to make a check, but only have the group needs to succeed. If half the group succeeds, it counts as 1 success. This works for the chase scenes, or the overland travel challenges, etc. but doesn't work for all cases.
Ironically, I think I did at one point design a really great SC. It was multi-tiered, requiring different types of checks at each tier, and was set up so that pretty much everyone in the group was assured of being able to provide useful input. Unfortunately, the first tier consisted of disabling the arcane runes warding the area and the Artificer promptly rolled 3 consecutive failures, the totals of the three rolls combined was 5 before modifiers.
Bringing this back on point to the original topic though, I really like the idea of the crystal pushing back. Failure could mean that the party still realizes that they need to go to the grove, only now they suffer a penalty against the psychic attacks rather than a bonus since the crystal has weakened their resolve and/or the crystal is also able to alert its allies at the Grove that the PCs are coming, so the allies get a surprise round in and are in prime position. Success gives the PCs a bonus to defense against psychic attacks and/or allows them a surprise round on the crystal's allies in the grove as they are able to supress its ability to communicate with them. Just a thought.