Do the benefits of mysqli warrant rewriting a large, working system?

[hayyan]

I apologize if this question is a duplicate. I have read http://stackoverflow.com/questions/1972298/mysql-vs-mysqli-in-php:\[quote\] Note: If you are using MySQL versions 4.1.3 or later it is strongly recommended that you use the mysqli extension instead.\[/quote\]Because we were using the old mysql functions, new code was thoroughly reviewed to check for SQL injection errors. It was reviewed by our staff, so it's possible we could have missed something, but I'm fairly confident we're covered. Because the system uses mysql functions at the code, new code must follow that convention; we can't migrate to mysqli as we go...Is there a benefit in rewriting the entire system to use mysqli instead? Or better asked, would the benefit be worth the fairly large cost? Or is this something we should consider when we do a major rework (in the next major version)? I'm of the mindset that if it ain't broke, don't fix it... but am I just being stubborn?