Yes, the Senate makes or breaks decisions regarding the people, so they should be elected. Not to mention they are being paid by the people so this is even more reason why they should not be merely appointed, but selected by those in which they will be somewhat controlling their lives.
The senate should be elected because we live in a representative democracy. We have had this system for a long time, and it has worked successfully. It's important that the electorate chooses its representatives so that they are accountable for their actions. If people are upset with their performance, we can elect new representitives at the next election.