Fellow shopping lover here haha, don't just leave an evening for Umeda. It is one of my fav areas and you really need to be there during a daytime to have time to look around it all.
Akihabara is far less electronics and far more otaku these days, if you like this try make time to go to den den town in Osaka too as it just as Otaku but much friendlier and less intense!
It is also better to go to aki at late afternoon/early evening night because all the lights will look better on the shops and most of the arcades and stuff come to life at night.
If you are not even the tiniest bit into anime/video games/otaku you wont "get" akiba very much and will probably just scratch your head at all the toy shops and be outraged/confused by some of the dodgier places and goods for sale
