Is there a way to erase your career mode progression and songs unlocked without losing your custom characters and downloaded songs? Or will erasing a band erase everything?
If you're playing Rock Band 2, you can delete a band you've made (though i'm pretty sure that will erase your career progress) but still keep your character. Also, any DLC or songs you unlocked in career will remain. Rock Band 3 i'm not positive about.
In Rock Band 3, the only way to lose your characters and career progression is deleting your save file. All the on-disc songs are already unlocked from the get-go.
The Spade Challenges in Rock Band 3 bug me. The difficulties are not even close. The overdrive ones can basically get fully cleared with 5 spades quite easily even on very hard songs, while the streak ones are unfairly hard. Example: I did a set with Crazy Train and Beast and the Harlot, two of the hardest songs in the game on Guitar. I got 5 spades on both with the Full Overdrive challenge. Then I did Foolin', a relatively easy song, and only got 3.5 spades in the Note Streak challenge, yet I 5 starred the song and got like 97% of the notes. Why does the difficulty have to vary so much? It's like how I do doesn't even depend on the song at all, it's just chance, based on what challenge I get.
A fickle crowd? Fridge Brilliance! But seriously, the spades are messed. Fortunately, you don't need every spade for gold, the golds are optional, and other bugs (like being able to pick "random" courses until you get something you like) help cancel it out for completionists.