noga のが

この本は読むのに簡単だ。This book is easy to read.
この本は読むのが簡単だ。This book is easy to read.

I was wondering if anyone could explain to me how these two readings differ in nuance?

As I understand it "no ni" highlights the noun, and "no ga" is highlighting the action. So

この本は読むのに簡単だ。

means that the book is simple to read. The book is written in a nice way.

In the case of "no ga" you are highlighting the action. So

この本は読むのが簡単だ。

actually means "the act of reading this book is simple". The book has a large font perhaps, or the pages are not stuck together.

Similarly:

声を出して読むのがうまい - good at reading aloud

ベッドで読むのによさそうな物 - a thing that is good bedtime reading