Exporting in Premiere from mpg 720 to h.264 1920
No. I assume your 720x576 video uses anamorphic pixels, making for a 16:9 resolution. Still, there is no added benefit to the higher resolution, as it won't increase the quality of your video. On the other hand, your video file will be much larger. Export in your original resolution with a high bitrate instead (not higher than your source material though). If you need to export an uncompressed copy, use a visually lossless codec such as DNxHD or Apple ProRes.

That is, assuming by 'loaded into Premiere' you mean this is the resolution of your source material. If you are referring to your sequence and your source material actually has a higher resolution, create a new sequence with the respective settings, copy everything from your current sequence to the new one and export that using the same resolution as your source video.