The Panasonic 8000 works by zooming the 2.35:1 portion of the letterboxed image in so that it fills your 2.35:1 (2.37:1) screen. The black bars are not gone, they are actually just projected onto your wall above and below your screen. Depending on your installation, these may be more or less visible. Some deal with this by putting black velvet above and below the screen, others do not find it objectionable and simply ignore it. DVD / Blu-ray menus will be projected onto the wall, however.
No, you do not need a lens for 2.35:1 unless your particular installation limits the lens shift / zoom capabilities of the projector to the extent that it is not physically capable of filling the screen properly in auto-zoom mode.
FYI anamorphic is the proper term, panamorphic is probably derived from "Panamorph," who is simply a manufacturer of anamorphic lenses (a company I also consult for, in the interest of full disclosure). Adding an anamorphic lens results in being able to use the full projector resolution and brightness for 2.35:1 content (1920 x 1080 pixels, vs. 1920 x 810 typically for zoom) and actually eliminates the black bars rather than projecting them onto the wall. The practical benefit of using a lens is a brighter image with greater pixel density compared to zooming, plus the actual elimination of the black bars. On the negative side, using a lens means that you lose the 1:1 pixel mapping of the letterboxed image.
Many people start out with zoom and eventually end up adding a lens at a later point to boost picture brightness and eliminate the bars. Others find that the zoom method is perfectly adequate and some actually prefer it.