It depends upon the name - I generally like -belle, -anna and -beth names.
I like Rosabelle, Amabel, Emmabelle, Kirabelle, Corabelle, Lilabelle....
I don't see them as the same as other "madeup" names. These are two real names combined, not random sounds shoved together. I wouldn't use them, though, because they probably wouldn't age really well. Maybe for a middle or a good GP list, lol.
I love Adabelle! Adabeth, too.
Name "smushes" can be iffy, but I generally don't think they sound made up, particularly when they have those typical compound name endings: -belle/-bel, -anne/-anna, -beth, -lee, -el/-elle, and so on. It's when you start getting into Reneesmee territory that the names start feeling made up and hopelessly awkward. There's a big difference, in my mind, between something like Christabel and something like Janisapril.
It depends. I can't stand most belle/bella names (totally overdone and just annoying to me now, sorry to those that like them). The only one I like is Annabel (spelled that way). I think names like Isabelle, Annabel, and similar are fine. Names like say, Gracibelle, Arabella, etc sound too cutesy and a little made up to me. Like, hey I like this name, let's throw "belle/bella" on the end of it so it's cute for my little baby princess!
But like I said, it really depends on the name. Some sound fine (even if they're NMS at all), others sound like a smoosh name.
Usually I love it, but Clarabelle, Adabelle, and Idabelle soounds weird to me. It's not that those are ugly names, I just (much) more like it as a single Clara, Ada, and Ida. Other variation but not with this -Belle.
However, I want to add Lucibelle. Not sure about the spelling but Lucy+Belle sounds pretty cute to me.
I think it depends, for me. I mean, I love Adabella and Adorabella, but Miabella and Carabella/Clarabella and Mariabella and such... too much for me. I do like Corabelle/Corabella, though. A lot of them are purposely smooshes, though, but they're mostly recognized now. I'm pretty sure that's how Annabelle/Annabel started, but now it's recognized as a well-loved and very legitimate name.
It doesn't say it directly, but I know I've seen on some site that Annabelle is a modern smoosh of "Anna" and "Belle". Not saying it's right, I just know I've seen it. And it seems like that's what that link was referring to (along with Amabel).