Another suggestion, if it isn't too late.
Are the EXTRA icons random or fixed? The reason I ask is that the other day when I played it I found the XTRA letters and then had to wait 3 levels before finding the E - in the levels inbetween I found loads of X's, T's, R's and A's
Obviously, I'd expect the letters found in the secret areas to be fixed, I'm just wondering if the ones generated randomly when killing enemies can be done so that they don't generate letters you don't need.
Oh, I know folks are asking for more levels, but perhaps if you made the level editor available (and more usable?) we could create our own extra levels
The concept being similar to Chu Chu Rocket (Dreamcast game). Many of us back in the day exchanged dozens of custom made levels. I have a memory card full of levels created by other people.