Piper Jaffray analyst Gene Munster says Steve Jobs’ physical appearance at Let’s Rock — a widely-anticipated Apple special event scheduled for Tuesday at 1 p.m. EDT in San Francisco — will reassure investors and boost the company’s share price.

In a note to clients Monday, Munster doesn’t claim to have any inside information about the health of Apple’s (AAPL) CEO, who had a cancerous tumor removed from his pancreas in 2004 (see “The trouble with Steve Jobs“). At his last public appearance in June (pictured right), Jobs looked surprisingly thin, setting off several rounds of speculation about what might have caused his weight loss (see here).

Rather, Munster’s belief that Jobs’ appearance Tuesday will be a “slight positive” for the stock is based on the assumption that Jobs would not be going on stage if he didn’t feel — and perhaps more important, look — well enough to reassure investors.

“We are confident that Steve Jobs will be presenting and we anticipate his appearance at the event to be viewed as a positive,” Munster wrote under the heading Steve Jobs’ Appearance Will Be Key. Apple has not confirmed that Jobs will speak Tuesday, although the Apple chief typically makes the new product announcements at big media events like Let’s Rock.

“While some investors are concerned that Jobs will not deliver the keynote,” wrote Munster, “we have reason to believe he will. Therefore, we believe his health has improved since the June event, which would be a positive for the stock.”

Munster goes on to outline his expectations for Tuesday’s event: a redesigned iPod touch and a new iPod nano along with price cuts and capacity changes for the shuffle and classic.

One “unlikely wildcard,” he adds, “could be updated AppleTV hardware features like live TV recording (DVR) or other digital living room accessories for the iTunes ecosystem (such as wireless speakers).”

For more speculation about Apple TV, see Tuning in to Apple TV 3.0