Yes, travel insurance is worth having for a trip centered on Plettenberg Bay, and the honest reason ties directly to what draws most visitors here: whale-watching boat trips, diving, kayaking, and hiking trails through the nearby Tsitsikamma forest and coastline, all of which carry real activity risk beyond an ordinary beach stay along this stretch of the Garden Route.
Plettenberg Bay has local hospital and clinic services for routine care, but anything more serious is typically referred to George, the nearest larger Garden Route town with fuller hospital facilities and its own regional airport, with further specialist care available in Cape Town if needed. Confirm your policy covers medical transport between Garden Route towns, since that referral to George, not treatment in Plett itself, is the step most likely to matter if something goes wrong.
Whale-watching and boat-based excursions along this stretch of coast are popular and generally well-run, but any boat trip still carries the usual water-activity risk that some general policies handle differently from routine sightseeing; check that your policy covers boat excursions specifically rather than assuming a land-based itinerary clause extends to them. The same applies to multi-day hiking on Tsitsikamma trails such as the Otter Trail, where remote, phone-signal-poor terrain raises the stakes of any injury beyond what a policy for ordinary day hiking might assume, and where rescue can genuinely take hours to arrive.
The Garden Route's dry season has, in past years, brought serious wildfire risk to this region, including major fires around neighboring Knysna, so trip-delay and evacuation-related cover is worth checking if you are traveling during a high fire-risk period, particularly for accommodation near forested areas. Keep any clinic paperwork, tour-operator incident reports, and receipts for treatment or transport if a claim follows, since documentation from Garden Route operators tends to be straightforward to obtain on request.