I am loving the idea of battling your inner self here.
I had an idea about a way to expand the idea of doing so.
Raise your hand if you remember what you had to do in Simon's Quest.
If you are raising your hand right now, then think of the reverse. Instead of having to find all of Dracula's parts and rebuild him, you would find all of Simon's corrupted inner workings (his heart, his mind, his eyes, his soul, his arms) and free them from the demonic power corrupting them.
This would in turn grant Simon more abilities (freeing his heart would allow him the power to use sub items, Freeing his mind would allow him to use skills, etc.) and also serve to give players a metroidvania feel: you COULD try and free his arms before you get the ability to use skills, but it is much harder.
Additionally, freeing them could be left to defeating a boss. Maybe for the eyes, you would have to defeat Paranoia (that clown from Dawn of Sorrow), seeing as how his entire gimick is manipulating what you see.
Just throwing ideas out there. Hope this helps with the concepts