At least you guys seem to agree on one thing, make it a sense upgrade -which seriously wasn't something I'd even considered, I was thinking of a whole new power, but see now that that would be "pointless" - all things considered.
As to which skill should activate the power, I still see a use for both, but I see the problem with that too - xp drainage and all. It seems to me that you guys won't agree upon which is best suited, which is fair really as both have good arguments for your positions. I think that past events might be best suited for discipline, while present might fit more for vigilance… as for future event, that is a tough one, because both could fit in my opinion.
Although the solution of just spending LS points might also make it more of a plot device and players might not so actively use it in the same way.
1 LS gets you the vague impressions (pain, danger, menace) for present, give nothing of future, as LS 2 for past;
2 LS gets sense of location or environment, perhaps even people and/or events going about, but still vague except such immediate things as danger, friends involved (names), pain and so forth for present and past, future as LS 1 for present.
3 LS is needed for unknown people, like a prey not known personally, but name, deeds done (cause for bounty for instance) and so forth, also items need this many LS to feed the force user with impressions (info gained from items as LS 2), future as LS 2.
4 LS gets you more definite answers about past and present events, but still vague of course, future events as LS 3 for past and present (same with items).
Of course, the future is always in motion as the saying goes, so even "definite" visions are not set in stone… as I said earlier, I usually used farseeing as a paranoia creating tool for large groups of players.
This way we can circumvent the skill use, I mean I would assume Anakin would have quite a bit in Vigilance and he couldn't make sense of the visions he received … you could put it down to roleplaying and stuff, but if he had 3 or 4 ranks in vigilance, and I wouldn't think that to be too high for someone like him in episode 3 at least, he still didn't know wtf he was doing and interpreted it in silly ways … he could of course botch the roll each time… but … by just using LS this way, one could arguably say that even if he had a force rating of 7 or 8 (he was the chosen one right?), rolling 7 or 8 force dice could still end up with few LS and tons of DS…
So, I'm reconsidering skill use - as I am really fond of skill uses for most stuff I must admit I'm now venturing into unknown terrain.
Using DS for this power, through strain conversion (or even the destiny point expenditure) could even colour the vision further into more desperate and dangerous ways… yes… I think I like this path. This way visions could also come to the player through the GM, he asks for a force roll and depending on LS/DS ratio - colours and tweaks the vision according to that… yes… HM… I think I like.