I listened to my copy of benefit earlier this week (Monday night?). Good stuff. I'd never heard the album before, so listening to the surround mix was distracted by listening to the music for the first time.
Frankly, the guitar parts on Benefit seem to add something to the sound, a bit more rock'n'roll, compared to TAAB. I must admit I cannot compare easily to Aqualung - it's been years/decades since I listened to that album (I think I have it on cassette), and I'm holding out for the 5.1 mix DVD/BD single-disk release (I simply cannot justify the price for the Collector's edition).
If you are even a mild Tull fan and like surround music, I think you'll like Benefit.
On a side note, I got into that prog groove after listening to Benefit, and threw on Quatermass right afterwards. My first listen of this recent 5.1 release about a month ago did not have much impact upon me, and I thought maybe it was just more "busy 70s prog". But the second listen changed my mind. More good stuff.
Sometimes you have to be in the mood, I guess...