A good question.
A local answer.

A central base keeps the Glenelg and city day simple; price the regional tour or car transfer separately.

Choose a restaurant close to the stop so the evening remains relaxed after a full tour day.

Check first transport departures and the airline's check-in requirement before choosing a cheaper but less convenient room.

Pair lunch with a neighbourhood stroll instead of crossing Adelaide for an unverified old price.

Pick the river section by the scenery and mooring options you want, then check the hire company's permitted route.

Choose one child-friendly anchor per day and pair it with a park, market or museum that works for different ages.

Compare the current timetable, total travel time and arrival location with flying or driving for your exact dates.

If open, visit when the stalls you want are operating and leave time for a meal nearby rather than treating it as a quick photo stop.

Take Glenelg as a separate relaxed coastal outing and check the current tram journey from the accommodation.

Choose two or three priorities and count the ferry or flight transfer as travel time, not an attraction day.

Check current ferry and airline baggage rules, vehicle needs on the island and change terms before committing to either route.

Use the remaining free time around Glenelg or the city rather than building another distant outing into a short stay.