What are your thoughts about moving up product line(s) within a Company?

Did that with Magico was very happy did that with ARC was happy as well.

Audio Note products are designed around this idea, especially their speakers. The various models of the E range from around $4000 to $200000+. They all use the same cabinet & design, and look the same. As you move up the line, you get better quality drivers, wire and crossover parts, and they are built & matched to closer tolerances.

I have 3 pairs of Zu speakers:

Omen Dirty Weekend MkII
Soul Superfly
DefHead

The Omen DW's are the most recent acquisition, really bought for fun more than anything.  I was kind of amazed how good they sound in comparison to my other pairs.  You really get a lot of the Zu sound at the entry level.  

I'd say at least in this case moving up the line allows you to fine tune your system a bit.  Maybe you want more resolution, more attack, better treble handling, smoother frequency response... maybe all of the above.  There is a speaker up the Zu line that can do those things.  What you have to be careful of is the models higher up the line will sometimes require more careful amplifier matching.  I have amps that will sound great with some my Zus and not so great with others.