Apparently, in Maya 8, smooth preview only works with NURBs and Sub-D. It was added for polygons in Maya 2008.

https://forums.cgsociety.org/showthread.php?t=563523

So, you can either use the regular smooth command and undo like you've been doing or the way I used to work in Maya 7 is to take advantage of poly proxy similar to what this guy shows:

https://www.imanishi.com/mayablog_en/...modelin-2.html

What I would do is adjust the proxy settings (when creating) so the smoothed mesh and proxy are output to two different layers, then just move the smoothed one over a specific amount (-2 in the z for example). This would allow me to to see how my edits to the proxy are affecting the smoothed version side-by-side. If the model/scene gets taxing on the computer, then turn the smoothed layer(s) off. Sometimes I like this more than smooth preview but it does take more to set it up. If you've ever watched SM's apache tutorial, that's the workflow that KB uses as he's building up the parts. Very handy.