Does Praying Really Matter?
Yes. It makes a person feel better, and that's what is important. A believer praying to God is like an ex-JW yelling or shouting at a JW Witnessing Cart. No Impact whatsoever in both, but it makes you feel better.
Where is the evidence?
It really depends on what you want to see as an evidence. A divorcee/single mom with two kids does two jobs a day to support herself and to keep her kids in school. She prays to God to give her strength to face the problems of her life. What evidence do you want to see if her prayers are being answered?