there's so much more to see... I figured I would've stayed in akiba more too but there were a lot of other places to check out.. you can only do so much shopping.
If you're into anime tora no ana, animate, melon books are pretty much the places you'd check out... once to get through the shock factor.. a second time to buy stuff if you don't buy anything the first time... a 3rd time if you go alone to buy stuff you don't want your friends seeing you buy. :P
A few game shops.. used, new, maybe you'll stumble into one of those places that has an ultra rare jp region game.
hobby shops like volks if you want model kits or dolls or model train stores... I basically wandered in and out of every store over the course of a couple days, sex shops, anime stores, video stores, arcades, electronic component stores. I stayed in a hotel in ueno so it was only 2 stops to get to akiba, and the food was better in akiba than ueno so after a day of wandering elsewhere in tokyo we would stop in akiba to grab a bite.
Echigoya's main store I think is actually in shinjuku.
I futz with V2s, V3s and V6s. I could be wrong... but probably, most likely not, as far as I know.