So, what lessons did I take away from the Midwest Massacre, especially as regards my Tau?
Aegis Defense Lines are a must-have right now: Easily one-third of all armies at the tournament were running Aegis Defense Lines, and I can't say I blame them. Between the extra cover available, the ability to lay a speed bump across a section of open board, and being able to take a twin-linked double autocannon with Skyfire and Interceptor, the ADL fills several gaps that armies can use to their advantage. Even the Tyranid player that took third place took a defense line (although without taking the gun emplacement) just to get the extra cover. I personally had a lot of trouble dealing with enemy fliers, so having the gun available would make a huge difference, and at only 100 points, it's not horribly hard to shift things around to afford one.
Prescience is totally worth it: Being able to grant re-rolls to any friendly unit within 12" of the psyker is fantastic; between that and Markerlights, I was able to make my shooting very reliable. Well, the hitting, anyway; making wounds stick was something completely different, but that's neither here nor there. I have no regrets taking a Farseer in my army. However...
Eldrad might not be totally worth it: Eldrad's a huge chunk of points, and if that chunk of points runs off the board or dies (which happened more often than not), I'm screwed in any scenario that uses Victory Points. While he brings a nice array of powers, I only ever used two with any frequency - Prescience and Misfortune. I also like Scrier's Gaze, but the timing on that power is wonky, since it conflicts with the rules as written and doesn't appear to actually be usable for Reserve and Outflank rolls. If I'm only using the Primaris power regularly and reliably, having all the extra powers doesn't really help me. Taking a Farseer instead with both Runes and one power costs just under half as much and gets me most of the same utility. I would lack the ability to use a power twice, but I can cope with that. The points saved can go into buying that Aegis Defense Line. I'll play around with lists both with and without Eldrad, and see how the power difference plays out.
Rethink War Walkers: I like the concept of War Walkers, but they're kind of a 6th Edition solution to a 5th Edition problem. Sure, it's easy to glance vehicles to death, but if there aren't that many vehicles on the board, they're less useful. Not useless, just not as useful. More often than not, they end up as a suicide unit, and without Scrier's Gaze or Acute Senses, it's a bit harder to guarantee they'll be on the side of the board where they'll do the most harm to the enemy before dying. I can't help but think that those extra 120 points would be better spent somewhere else. Also, with Interceptor guns on the table, they tend to disappear as soon as they appear. That makes starting them on the table the better option, and at that point I might as well buy a better unit. I'll still give them some more runs on the table, though, to see how they do; they do bring a nice volume of fire, especially against hordes.
Tau Pathfinders are awesome (I finally admit it): I've hemmed and hawed about whether or not I like Tau Pathfinders, but in 6th Edition I finally have to admit that they're the best Fast Attack choice we have, as well as the best way to get Markerlights in volume. In 6th Ed's vehicle-light environment, making your shots more reliable is better than having a pair of suicide melta speeders. I still wish there was a way to take them without the Devilfish, but even then they're still worth the points. Also, they're still helpful with flyers; even though they can't raise BS on snapfire shots, they can still eliminate cover saves, and that includes those Jink saves from flyer evasion.