I always upgrade my iPhone because I always give my "old" one away to my parents.
I am still using a late 2008 MBP though, and I will probably get another year out of it as I recently put in an SSD and upgraded the ram to 8 GB. It runs great! No complains about it at all... I think the feature that attracts me the most of the newer MBPs is the retina display but I'll probably wait for Skylake or a redesign (which we'll probably get soon).
With the iPad, I began with a 2, then upgraded to the 3, then the mini, and now the Air. Don't see me updating my iPad at all unless a must-have feature comes along (you never know). The Air is the perfect size, hence why I am upset with the crack.