Mark,
I've played Barton Creek Crenshaw 3-4 times and Spanish Oaks once.
I find the Crenshaw course to be a lot of fun, but it has it warts. It's a bit of a juxtaposition between Texas Hill Country and Parkland golf. It doesn't do the Hill Country bit as well as it's neighboor course - Fazio Foothills - although 17 and 18 are good examples of the genre (fairly severe elevation changes, combined with carries over densely vegetated ravines). Tom is correct in that there are a decent amount of blind, or semi-blind shots. Some work, but some don't such as the drive on 1 and approach on 2 (the worst holes on the course for me). But the middle of the course enters into more parkland type of land. There is still elevation, but the slopes are gentler, and it's here the design starts to shine. While the fairways are tree lined, there is lots of width. Finding the right side of the fairway gives the best line into very large and tilted greens that fallaway as Tom indicated.
This is the strength of the course, as the ground game is in play and with the size of the greens you can watch your ball run a long way towards the hole. There isn't much in the way of contour on the greens and C&C certainly have built much better greens since then. But the tilt and size are what present the challenge. I like the course quite a bit more than most that play it.
It is certainly the red headed step child of the resort. The condition is more spotty than the other courses and the greens have more grain. There aren't as many hero chances either, which appeals to many looking for a hill country golf experience. Those are the reasons it doesn't get as much attention from guests as the two Fazios on property. My buddy golf trip went to Austin last summer and the Crenshaw course was the least favortite we played by the mostly retail golfer crowd. They spent a lot more time looking for balls in the gunch on the Canyons, and the round was much quicker on the Crenshaw as a result, but they like what they like. On the property I would go 1) Canyons 2) Crenshaw 3) Foothills. The vast majority would put the Crenshaw last.
It's been four or five years since I played Spanish Oaks, so my thoughts will be briefer. I know that I really liked it. It belongs in the discussion of best in the Austin area, along with Austin GC, Escondido and Austin CC (although many here would not like the severity and forced carries of the back 9 at ACC). I remember liking the routing a lot. I remember a couple of good par fives, a really good short par 4, excellent conditioning, challenging greens and a forced and disappointing finishing hole. More subtle elevation here also, but there is a good amount of change between the highest and lowest part of the property. Well worth a play for sure.