I agree. User created strings would be phenomenal. That way, save data and scores could be stored and take up less space without limiting the number of strings that can be used. Having access to an unlimited number (memory permitting) of user created strings would be first on my list. I also would really like to be able to edit a specific character of a string, much like lists, without having to do complicated sub( routines that congest my code and take up space. For instance, Str1(4 would refer to the fourth character in str1. Yeah, I know, it's exactly the same as lists, so why not just use a list.
The reason is that storing to lists takes up more space than storing to strings in more ways than one. Also, I believe that strings are generally faster than lists, but I might be wrong.
Other things I'd like to see:
More Finance Variables
Access to multiple graph buffers
The option to activate and deactivate that whole thing with math print and the mode screen text that interferes with vertical text sprites.
That's all I got for now…