The trip was in October.
I think it's probably easy to avoid the buffets. I just didn't put my foot down at the first one like I probably should have. If you do an organized thing with a private guide I think you could let them know your preferences up front. And if they try taking you to the shops just tell them you're not interested.
I actually liked Yogya a lot on the whole. But I think that was mainly because I clicked so well with my driver Rocky. It was really freakin' hot though.
As for what I would do differently... I might have tried harder when it came to the meals to elicit more options. And I wouldn't stay at the Phoenix Hotel again. The breakfast was really great but otherwise I would have preferred a more modern place I think. There are a couple of brand new, very grand looking hotels in town. And clearly I would have scrapped the whole plan for the day when we went to Merapi. I'm not sure the temples at Lawu would have been a better choice given the 6 hour round trip drive. But I think there might have been some other things that I might have done instead.
Borobudur sunrise is a must IMHO. Once the general admission hours start it is lots of big tour groups, buses full of students, etc. I was there on a Saturday. I don't know if other days are less popular or not for the sunrise thing.
I'd also say get to Prambanan at opening if you can swing it. While the light was good when we got there it was already getting hot. Apparently there's also some kind of culture show right next to Prambanan at dinner time so you can see it at sunset. But the park closes before sunset. I think they light it up at night too. I wish I could have shot some pictures of that.
As for Bali, again I might have tried harder to get better lunch options. I might have also asked some more questions about the timing of things. Like the last day, we had like an hour and half to kill at Uluwatu before the Kecak performance. Had I known how much free time there would be in the schedule I probably would have stayed longer at the culture park.
I think I might also have gone to one of the "cultural" performances in Ubud too. There were kids selling tickets on the street to various shows. I didn't want to be bothered at the time but now I think it might have been fun.
But if you go on your own without bothering with guides and drivers you can do whatever you want with regard to the shopping trips and places to eat. I just think having a guide can be really helpful in places where you don't know the language or culture.