I beleive as a senior tester, we should fully understand the product we are testing aginst. Knowing the direction/future of the production is the first step of creating the best tests.
We should be actively involved in project/product planing, and make impact on the strategy of the product (not the test). Note, this is one of the important way which we can improve product quality.
Being involved on production design can also help us enhance skills about manging/build a project. And enhance our technique skills which is cruicial for Test Architect and Domain Expert career path.