What is it about traditional calculator UIs that you don't like on mobile? I think they work great, unsurprisingly, since the form factor is similar. I have several (paid) mobile apps that fully emulate a traditional calculator model and I regularly use them.

To give some positive feedback: I like your loan calculator. That's something that could really be useful for a lot of people. I think there's still more you can do there, eg let people figure out how much credit they can afford with a given monthly payment. Take a look at traditional financial calculators like the HP 12c, they're extremely versatile in that regard.

Personally, I don't see the need for separate calculators for things like percentage increase or rounding numbers. Most of those could be combined in 2-3 apps at most, imho, scientific, financial and unit conversion. The others are really separate apps that would need a lot more functionality than the pure calculation aspect to really be useful (eg time tracking).