"Trust But Verify"?
Well, that's all very well if you trust the President, both to actually want another Scalia or Thomas, and to know how to pick one. If he'd named Kozinski, or McConnell, or someone like that, we wouldn't have to trust either his intentions or his instincts, since we'd know what we were getting. But with Miers, the President is trying to sell us, you should pardon the expression, a pig in a poke. And I'm not sure that he actually wants another Thomas, or that he knows what it is that makes us like Thomas, let alone that his judgement that Miers will fit the bill is sound. And if she isn't, it will be too late. All confirmations are final. We won't be able to return or exchange her.
That said, the Senate ought to confirm her. The constitution leaves the selection of judges to the president. The senate is not asked for its advice, but only for its consent. The senate is not a partner in the process, in any sense, and is not entitled to express its preferences. Its only role is to act as a check on the president, in case he nominates an incompetent or a crook. And the fact that the senate's consent is needed will almost always dissuade the president from doing so, so in almost all cases the senate ought to be a rubber stamp. Miers appears to be honest, she clearly knows the law, and the president chose her, so she should be confirmed.
The framers of the constitution never dreamed that judicial nominees would actually be called to appear before a committee of the senate, and be questioned on their views. That is a modern practise that began during the death throes of segregation, when Southern senators wanted to try to prevent the appointment of anti-segregation judges. Perhaps it's time the practise was abolished.