I'm a big fan of MW1. I was an early adopter and have been using it daily ever since. I think that the app has been value for money and would like to upgrade to access the new MW2 features but also to support your business. However, I didn't go ahead and upgrade yet because I know it is a one way migration and tbh there are some fairly negative reviews in the AppStore, particularly with regard to performance on older iOS devices. I run MW1 on an iPhone5S so no problem there but also on an iPad Mini and that is the device I suspect may struggle to run MW2 (it is already a bit sluggish with MW1 and I would not want further degradation). You don't seem to publish minimum hardware requirements so should I expect performance of MW2 to be better, the same, or slower on iPad Mini?
It's hard to tell as it really depends on each device individually. From what I can tell for sure, is that we have significantly improved the performance and stability of MoneyWiz 2, since the first release. Moreover with the next 2.0.5 update some of the performance issues will be fixed specifically for iPad devices. So answering your question I think there will be no difference (or at least no big difference) in performance of MoneyWiz 1 and MoneyWiz 2 on your iPad mini.