Because I am an expert on Oracle development tools, I'm often asked for advice on technology migration projects, typically from Oracle Forms. Most of these projects originate in the IT department, and they often fail the simple test of business justification. Simply: Does the benefit justify the cost?
The maximum achievable benefit is limited by the difference between the current technology and the proposed new one.
Changing your application from Oracle Forms to Oracle APEX has a short technology distance: From one PL/SQL based, data-driven monolithic application to another. The only difference is that APEX will run in a browser without the Java plugin, for example in mobile. Because the technology distance is short, things can't change much and you can't justify much cost.
Changing your application from Oracle Forms to Oracle ADF has a longer technology distance: From a PL/SQL based, data-driven monolithic application to a Java-based, UI-driven, modular architecture. The technology distance is much greater, meaning that you can do completely different things with an ADF application than a Forms application. The potential upside is much greater. Whether you are able to realize it is a different matter.