From every person I've talked to Laos has been their favourite part of SEA, so I've considered adding an extra week, but I do have a few extra days to play with either way.
Here is a general idea of what I was thinking for my itinerary, I've included traveling days and places I have to cross through, I'll be flying in from Hanoi to Luang Prabang , just looking for any reviews or aid on my itinerary. Main places I wish to see are Luang Prabang, Vang Viang, Vientiane , and the 4000 Islands.
Hanoi > (1h Plane) Luang Prabang [26th, 27th,]
Luang Prabang > (5h Bus) Vang Viang [28th, 29th]
Vang Viang > (4h Bus) Vientiane [29th, 30th,]
Vientiane > (10h Sleeper Bus) Paske [31st]
Paske > (2h Bus/3h30 Boat) Champasak [31st]
Champasak > (4h Bus/5/8h Boat) Don Khong [1st, 2nd,]
Don Khong > (1h Bus/1h30 Boat) Don Dhet [3rd, 4th,]
[Xdays: 5th, 6th, 7th, 8th]
I would not go to Don Khong AND Don Det. Choose one or the other. Instead I would make a trip from LP to the Plain of Jars. Alternatively spend a day or so in Savannakhet; this is really quite a charming town and is often ignored.
Savannakhet was one of my least favorite places I've visited in Laos, but I think I may be in the minority there. Even so, it is definitely worth an overnight stop and is the logical choice for breaking up the long bus ride from Vientiane to Pakse, unless of course you are anxious to knock out the grueling overnight bus ride you mention.
I think Rufus suggestion to pick one of the "Don"s and stick to it is a good one too. In fact, the only thing that bugs me about your planned itinerary is that you are moving around too much and not spending enough time in places once you get there.
If you've got those X-tra days available to spend [Xdays: 5th, 6th, 7th, 8th], then I'd definitely spend the extra odd day or two in the places you will visit. At a minimum, spend a few extra days in Luang Prabang. Just remember that getting from A to B takes more time in Laos than elsewhere, and you don't want to spend the entire trip on a bus. Regards.
" Savannakhet was one of my least favorite places I've visited in Laos."
I am curious as to why Exacto. Did you do the loop around Savannakhet and visit the temple with the ancient Pali scrolls and the monkey forest? There is also a dinosaur museum in S that is well worth a visit. It is a pretty quiet place, but I really like the town.
For me, one of the great joys of Laos was its slow paced way of life. You need time to enjoy and appreciate that. I had 2 weeks seeing a small part of Northern Laos - started in Luang Prabang ended in Vientiane, with a diversion up to Nong Khiaow. Its a fabulous place, but rush it and I think you'll miss the point. I really wish we'd allocated more than 2 weeks even for the small part of Laos we saw. Your itinerary, to me, is way too much way too fast.
You are right, Rufus. My lack of appreciation is subjective. Plus, I didn't do those things you mention, so it is fair to say that I didn't give the town a proper look and missed the highlights. As I've mentioned before, the place isn't charmless. I had a wonderful wander through the old downtown area and up along the river. But Savannakhet just didn't seem as charming or as typically Lao friendly, at least to me on those particular days, as the many other Lao towns I'd visited before or since. "Least favorite" is also relative. I still enjoyed Savannakhet, just not as much as Vientiane or Pakse or Champassak.