First in terms of holding its value, this would partly depend on your local market but I think the last figures I saw (Ferrari Market Letter) showed that these models had pretty well bottomed-out over the past couple of years. Maybe a few % value change either way of flat, but I will check & post again later.
Second, reliability does seem good from what I've heard, and probably best on the most recent models.
Finally, size is a moveable feast. I am just under 6'1" but am of the "long arms/long legs" variety, whereas others may have a longer body & shorter limbs. I rarely have problems with headroom in cars but sometimes can't get the wheel far enough away. I've never sat in a 328 so can't advise there but have no problems with the Mondial, but there's no alternative to finding one & sitting in it if you want to be sure you can fit AND be comfortable AND can properly use the pedals & wheel. Good luck!