I have the Saab upgrade, and my fuel consumption is unchanged - I was averaging 35mpg tank-to-tank cruising at 90-95mph in German in the summer.
As to suspension, I personally think the Eibachs are too hard for a family car. Yes, you will definitely notice the difference and the car will be soooo much more driveable
, but there is a definite tradeoff. Mine is a standard car which initially had the 15" wheels with 65 profile tyres, and the ride was just about OK then. However, it was brilliant with a fully loaded holiday car - perfectly damped and little body roll. This says to me that Eibach have got their spring rates set too far towards handling rather than comfort.
Since I fitted the 16" wheels with 55 profile tyres, the ride in the rear particularly is not to my liking, but once again, the drive improved. You pays your money and takes your choice. It would be worth trying a couple of setups before deciding - some people have commented that the Abbott suspension upgrade is more comfortable I think.
It's also worth saying that when I left Trent Saab after having the Eibachs fitted, I was horrified at the ride - I thought I had ruined a perfectly good car. However, they settled down and smoothed out over the next thousand or so miles.
On balance, I'd say I was a bit disappointed. If I was upgrading, I'd look round and try more options before deciding.