I think this would be a good addition to the IDE. For tabs to spaces there is always the 'expand' DOS command, but having that in the IDE would be convenient too.
edit: even a show tab option to see what tabs need manually changed to spaces would be a good start, although indenting with the tab key would still be an issue.
It's mostly alignment issues with tab size of 3 vs 4 (for example) and with hosting repos and using code viewers that default to (and often cannot be changed from) the standard 8. Incidentally the hosting issue can be fixed (in terms of display) on a per browser/per site basis by using a plugin to change the CSS. There are manual workarounds for fixing after the fact, but it's natural to press tab to indent so I can't retrain/restrain myself from creating the issue in the first place (not that we should ever be forced to press space 24 times, instead of a few tabs).