As a current 156 owner too I can say I find the 156 has a comfortable driving position. The Alfa GTV I had before that was a lot lower position but still comfortable and previously I have owned a VW Sharan. The Sharan was a bit too sit up an beg for me. Having sat in the Altea it felt a natural position.
The extra height of the Altea gives a bigger car impression, I wouldn't say it felt any way smaller than the 156, if anything the opposite.
The 156 has been great but I do want the practicality of a hatch again. My wife has a 147 and we always use that for difficult to load stuff but it is a bit too small.
My kids are getting older - I have done the Astra Estate, Rover 800 and VW Sharan stuff for carting around prams and stuff. The Altea XL may be a better choice than the standard Altea for doing that, I think it is a good shape too. The XL will be a far more practical choice than a Sportwagon. I tried to convince the wife we should get one long before I finally got the 156 I have now when we still had small kids to ferry around with all the gear and it just wasn't big enough with the seats up.
If I needed the extra space I would seriously look at the XL. Practicality without having to go down the dull looking mini MPV or Estate route and a reasonable drivers car with it. If you like the Italian styling the SEAT seems the next best choice IMHO.
My personal view is that Alfas are trying too hard to compete with BMWs right now and have lost a bit of the Italian personality in the process. As its new German Chief Exec, Karl-Heinz Kalbfell, a former director at BMW stated; "you cant find financially-minded people in this company it's full of engineers, who all want to launch new cars and dont want to deal with the boring bits in between. Perhaps Alfa has a little too much spirit for non-Alfisti, in its appearance, driving style and temperament." That is what I loved about Alfa, being run by guys who love to make cars rather than make shareholders happy, though I guess to survive maybe Kalbfell was a must, I just hope they continue to make cars as stylish as the 156 was back in its launch days.