If you used sub-pixel alignment, it might be worth it.
I just wish we could get 300dpi displays for our computers already, and stop worrying about the pixel grid. But, we're going to need some better techniques for resolution independent UIs before that happens. In particular, you will probably actually need better hinting for vector based UI graphics, so that the same vector graphics that can be used for high resolution displays can also be used for lower resolution displays while still looking good.
It’s worth it to use some inter-letter spacing anyway, even if the spaces can only be whole numbers of pixels, because it avoids exceptionally wide or narrow word spaces.
I just wish we could get 300dpi displays for our computers already, and stop worrying about the pixel grid. But, we're going to need some better techniques for resolution independent UIs before that happens. In particular, you will probably actually need better hinting for vector based UI graphics, so that the same vector graphics that can be used for high resolution displays can also be used for lower resolution displays while still looking good.