I actually got MM for my birthday, but I had to basically buy it myself. Is your DW a photobook person or someone who prints pictures a lot? If so, I bet she'd love the MM like me! I'm so excited to not have to lug my giant camera around all the time. Can get good pics with MM and with the cellphone without the hassle/risk of taking my good camera around with me for a week. We do plan to do a lot of characters since DD is only 2. If you're mainly going to ride rides, there wouldn't be too many MM opportunities, but you do get ride videos and pictures which is neat.
I don't know anything about the fireworks cruise, so I can't speak for that, but I am a MM fan! In summary, I'd say do MM if she's a printed picture or photobook-making kind of person. If she's only going to post a few phone shots to Facebook, not-so-much.