An impressive example of what you could do with macros is LINQ - a static and type-safe DSL for querying collections of any kind. People did impressive things with it, like offloading the work to the GPU.

Another example would be about adding your own improvements to the time-system, improvements that are actually going to help you keep the code safe. Like the units of measure from F#.

However, adding powerful macros to a language that was not designed for macros and that is NOT simple ... I do think it is a bad idea. I'd be happy to see in Scala something like the code quotations from F#. Anything less is useless, anything more will make Scala way too complicated.