neat topic here.

It certainly is an interesting balance finding out what equipment one is comfortable with vs keeping the weight down as much as you can to make the ride more enjoyable vs how much cost.
Growing up doing canoe camping and having to lug packs over portages certainly taught me to appreciate less weight on my shoulders, and as I am not a big strong guy (younger or now) I have always certainly noticed less weight when going up long hills.

One aspect that I think is a real factor for a lot of people is the cost of having lighter stuff like a tent. Yes, this doesnt apply to only taking minimum clothing--and the error of taking too much clothing and/or heavy clothing is always going to be an issue with people who don't have self propelled camping experience, ie who have only car camped and never had to carry all the crap they take.
Cost thing I'm thinking of stuff like a tent, my example is probably pretty common-for years I had a 3 person tent (really a two person tent) because thats what I had (even single, hoping to meet an outdoor type of gal) and so it weighed probably 6.5 lbs easy, but its what I had and I wasnt going to buy an expensive one person tent, I always preferred to use that money on other stuff or to put towards a flight somewhere.
Clothes are fairly easy to chose light stuff and keeping the actual amount of clothes to a minimum, like you all have said, multi use and layering works fine for all "summer-ish" type temps we will usually see when bike touring, and even for a skinny guy like me who doesnt like to be cold, layering up can keep you comfortable.

re tools, and going back to the spare cable question, this is where being familiar with your bike and having repair/maintenance experience really makes a difference. Having hands on experience and really knowing your bikes condition is really going to make a difference of not having a mechanical problem. New cables, tires in good shape, and all of this stuff on a bike you ride regularly and not changing cables or whatever the day before you leave on a trip means you know everything is working fine beforehand with confidence--ie no need to take chain whips, cone wrenches or whatever- and yes, I figure I'll just get a lift somewhere if it is ever needed. So far my bike prep has meant I've never had a surprise needing a lift, so I'm sticking to what I've always done in the past, which translates into keeping the tools and parts list to a minimum.

Nuns mentioning of a cross country trip certainly made me think that with his RS setup and total bike/load weight, this will certainly make a real difference in days and days and days less traveling on such a long trip. For anyone, we tend to have a certain power output that we are comfortable putting out for all day, and especially day after day. Yes we get stronger over a trips duration, but for a given power output, pushing a 40lb bike/load combo is always going to be a bit faster than a 70lb bike/load combo, especially with all the ups we hit every day depending on the terrain. So it certainly makes sense to me that if you can cover lets say 25km more per day on a lighter bike expending the same amount of energy (a number I completely picked out of the blue), imagine how this will add up over many weeks--600km per month easy, and its not even meaning that you are pushing yourself more.
Could mean a cross country trip time could be easily a week or two less than on a bike with 40lbs of stuff, plus you save on accommodation, food costs.

I still think that for everyone there will be some doo-dad, piece of clothing, an inflatable pillow or whatever, that makes a comfort difference that is worth taking, but maybe because I'm getting older I can certainly see the attraction of getting the load weight down and finding your personal balance of weight/comfort/cost.