It's not the experience, it is how they are portrayed. If you want to make a complete blank slate to learn and grow with the audience, sure. But you need to make him/her likable and unique of his own. You need to show he has some base skills at least to come into play later perhaps (think Luke's Skyhopper experience) and grow. This makes a very connectable character that becomes quickly iconic. How not to do it is explain him in a couple sentences and show it off, making him/her ignorant, not inexperienced.
Meanwhile an experienced character works the same way, but it is much trickier to pull off. Even if he/she is experienced he/she still has to learn something new to grow and not plateau in the story. Even Vader who kept a cool steady level of power grew emotionally in the end of Episode 6. James Bond learns how to figure out the mystery in front of him, so even the most experienced characters don't start at the same level they will be at the finale. This is storytelling 101, that with any level of knowledge, they must learn and grow almost the same way as an inexperienced character.
What I am trying to say is that there is a debatable level of importance to the past, depending on the story, as long as the character grows in the story itself.