I recently did a project of a series of stills in V9d as an SD project. It is shown on a HD monitor and on some such HD's grey sections appear immediately outside the pic's left and right, with black beyond that to the 16:9 monitor edges.

So I figure why not rerender to HD 1080 50i to see what happens. Will it make for a sharper viewing experience? Please let me know what you have experienced on a similar project. Thx

To get it to fill in the edges, you really only need to render as widescreen. That should take care of that issue for you. However, if you're changing it to widescreen it's just as easy to change it to HD. But if you're going to standard DVD, you won't be gaining anything as you'll be going back to SD in the end. So it all depends on several other factors.

Now for the bad news... you'll need to go back and adjust EVERY image on the timeline. The pan/crop on each will be set to your original project properties and will need to be adjusted on each image to now match the new project aspect.

To follow up on Edward's comments, if you haven't done anything (i.e. no FX of any kind) to the stills, click the first one, open Pan/Crop, right-click and select Match Output Aspect, copy it, click the next event to select it, right-click and choose Select Events to End, right-click one last time and choose Paste Event Attributes.
That should take care of all your grey areas.
These are because of the difference between the square (1.0) and rectangular (0.9091) pixel formats.

Or, if you haven't done any cropping to the HD footage in the SD timeline, just change to the appropriate (1080 or 720) project template in the same frame rate. There will be no more black lines.

The reason you see black lines on the left and right with HD footage in an SD widescreen project is because SD widescreen isn't exactly 16:9; it's a little wider. The HD footage is exact 16:9. When you go to an HD timeline, the image and the frame match.