If I could give my honest opinion, I say take it to a local reputable repair shop and just have the display replaced for cheaper than a new Z30 and a Z10.
I'd rather pay for a screen replacement than to literally downgrade.
I couldn't squeeze a day out of my Z10 with all that I do, and from the sounds of it, you won't either.
Stay with the Z30, and simply have the display replaced. Much more cost effective, and that way you aren't sacrificing battery, ability, and design.
Good luck with your choice! Thanks for posting!
EDIT: My bad for jumping the gun to reply! Hopefully your new Z30 will last this time
