For the examples you gave, you can use SUBSTITUTE to create a new numeric data set which you reference for your graph. You can hide these rows if you wish.

For your x (assuming there are only ever *'s)
=SUBSTITUTE(A2,"*","")+0

For your y (assuming only ever * or < )
=SUBSTITUTE(SUBSTITUTE(B2,"*",""),"<","")+0

You do say that you have superscripted numbers. You can't get rid of them with formulas, probably with VBA. You might want to start a new post in Excel Programming and link this post to it.