We use our monitor stacks too. Our computer is outside and there's no way I could hear Gab if she woke up while I was surfing BB if we didn't have our monitor.
Those that haven't used their monitors for #1, keep it for #2 JIC. While the new baby is sleeping, you might want to take the older one outside so it might come in handy?? Otherwise you could probably sell it on ebay or something?? LOL

Ok... useless things for me:

#1 - the change table. I did use it quite a bit when Gab was a newborn but now I don't use it at all. So yeah, I could take it or leave it. It definitely wasn't a necessity.
#2 - size 00 dresses. Gab was crawling so she didn't wear half of the beautiful little dresses she had! It's only now, when she's walking, that she can wear dresses and she's grown out of the size 00!
#3 - baby powder. I got given so much and I haven't used it on Gabby once because it's actually bad for their skin.

I agree with Fletch... don't spend a fortune on a bouncer. Just a nice, simple one will suffice. I was given one so I didn't have to worry about that. Also, don't spend a stack on a high chair. So long as it is safe and does all the things it needs to, you don't have to have all the fandangled bits and pieces. It's harder to clean if it has more crevices!! LOL

I would more inclined to spend money on a good car seat (if it's second-hand, make sure you know the history... has it been in an accident before?) and a pram because they do a lot of mileage!