I can't help you with anything outside of Bali, but I think you are wise in only bothering to go to Ubud since the rest of your itinerary includes a fair bit of beach time at (from what I've heard) are much better beaches than those on Bali--Tanah Lot could be visited on the way to or from the airport.
Ubud can be very relaxing and might be a nice way to end a trip. It also has some pretty good shopping so you could wait to buy most of your gifts and souvenirs there.