"It might be worth a lot less if it just plain didn't work coz you didn't fix it. So might be worth a shot. Paperweights are worth less than working phones."
You can always get an "out-of-warranty" repair, which consists of taking your old phone and handing you a new (refurbished) one. If you botch your non-working iPhone to the point where they refuse an "out-of-warranty" repair, then you did indeed cost yourself a lot of money.
(My wife's first iPhone was given to her by a relative, complete with broken screen and speaker not working, we took it to the Apple Store, paid £140 for an "out-of-warranty" repair and she had a new phone. Much cheaper and better than repairing it).