Hi,
It is incredible that you have not thought of a function to update the price lists...
We have in our TODO list a feature for mass actions on products. But this feature would require some development time and does not have a schedule yet.
After that, it's not that we do not thought about such feature but, there is very very few people who asked for it.
So, we focus on major features.. And I don't know a lot of shopping cart which have such feature.
After that, you can export your products and make a massive price modification with OpenOffice of Excel ; and then, import your new product prices (with just the column "product_id" and "product_prices").
Regards,