Machka, we are kindred spirits, and this post was enlightening1) When I travel, the weight of the bicycle + bicycle box + all the gear has to fall within the airline restrictions.
If I'm flying with Qantas, I've got a restriction of 32 kg per item, and I can carry 2 items. Other airlines have tighter restrictions. Some restrict you to a weight of 23 kg per item ... so that's usually the number I work with.
So after I've weighed the bicycle and the box ... whatever is left is what I've got to work with.
That is a very real cost, in monetary terms, of what you bring. If what you bring exceeds the limits, you pay.
2) My own personal guideline is to bring no more than half my body weight. Bicycle + All The Gear should add up to no more than half my body weight. From my experience, when I go over half my body weight, I struggle and the tour loses its enjoyment. I struggle cycling up hills, I struggle pushing the bicycle up hills, and I struggle during the off-the-bike lifting and carrying portions of the tour. Half my body weight puts me well within the 23 kg * 2 item limit ... so that's good too.
3) I mentioned the off-the-bike lifting and carrying portions of the tour above ... our tours are rarely the type of tour where we wheel the bicycles down the driveway and set off, then camp the whole time. Our tours usually involve flights, trains, ferries, hotels, hostels, and all sorts of things. When you've got to haul stuff around an airport or train station ... when you've got to dash from one platform to another in a train station ... when you've got to carry it all from the airport or train station to a hotel ... when you've got to haul it all up flights of stairs to your room ... you start to appreciate the idea of carrying less. In fact, you start entertaining ideas of mailing it all back home and travelling with a toothbrush and a towel.
You mention enjoyment ... and yes, that's a factor. I want to go as light as possible, because that is more enjoyable. But not too light that I'm missing a key element.
You mention speed ... I don't care about that. I rarely travel with an itinerary so tight that I have to reach a certain place by a certain date. All I know is that if my stuff weighs too much I find it very difficult to get up hills. And, as mentioned above, I have a pretty good idea where that line is for me.
As for specifically what I bring ... that list of stuff has been refined through years of cycling, years of camping, and lots of cycletouring. But, of course, it still goes through changes before each tour.