I'll admit it, I have an Amazon wish list. I keep it for myself, so I can add things that catch my eye and make me go "Oh, I'd really like to get that when I have more money," because if I don't make a note of it somewhere I won't remember what it was I wanted to get when I finally do get that extra splurging cash. It comes in handy when someone asks me for gift ideas, because then I can pop over to the list and pick a few things in the appropriate price range so they have some options. I also use it to make shopping lists over the holidays since I do most of my shopping on-line and I get super cheap shipping. The list is viewable if someone wants to look for it, but I don't advertise its existence.
I don't really see how simply having a list makes someone gift grabby, unless they're e-mailing it to people unsolicited or waving it around under people's noses without being asked for suggestions.
As to your mom spending too much money on your siblings... that's really on her. Yes, your siblings could make more of an effort to come up with some less expensive gift suggestions, but your mom is the one in control of her gift giving budget and your siblings aren't twisting her arm to force her to spend $700 on them.
If it makes her happy to spend that much money giving her family what they want, and she's not coming to you asking for extra cash to cover the mortgage payment that month, then why is it any of your business trying to dictate what she gets someone else as a gift? My husband and I know that if we asked for it, my parents would probably
be willing to buy us a very expensive gift or two for Christmas, but it
makes me uncomfortable asking for things like that, so we don't.
However, I don't police what my parents chose to give to my sister and her boyfriend because it's none of my business if my mom were to decide to spoil my sister with a nice TV because it's my mom's money to spend how she chooses.