I'm pondering as well if I should get a folder bike for short 3/4 day tours since I travel some through work and I enjoy adding a weekend or more to do something fun. Initially I was thinking of the Bike Friday NWT.
On a trip to Seattle I rented an older model BF from a bike shop and took it on a three day tour around Purget Sound. It was a great trip and the folding bike did quite well. The bike shop installed a rack for me but I again noticed the importance of fenders on wet roads. The gearing was great. I didn't knew Seattle was that hilly. The only issue is through the constant shifting with the grip shifters which caused a tear from the shifting strain between my thumb and index finger. Direct links to my tour blog with the Bike Friday although it probably isn't that valuable in deciding a folder:
day 1,
day 2&3.
The reason why the BF NWT failed for me is that folding was to troublesome once rack and fenders are installed. I wanted something that keeps things simple enough to fold/unfold at the airport and start riding from there. Now I'm eying the Brompton. The folding is much nicer and the bike is more compact. Still wondering a little about the gearing which would either be the standard or reduced 6 speed. I got to test ride one a little bit but that was all on flat ground. Unfortunately my local Brompton dealer isn't keen on renting one out.
The Ultimate question for me is will it be worth it - i.e. will it be useful and simple enough to take along on airplane trips and be able to tour somewhat comfortable so that I actually use it.