Your objections to an IGH are well founded. Yes, it's more difficult to change a flat (although really it's difficult getting the wheel back on correctly. Taking it off is relatively easy.) The main annoyance is having to get the chain tension right. If it's not exactly the same as it was before you took it off, the shifting will also need adjusted (not more than a turn or two of a barrel adjuster though.) That, however, is one of the advantages of the IGH. Extremely easy to adjust gears. For my shimano nexus 8, I put it in 4th gear and twist the barrel adjuster 'till the lines (on the hub) line up perfectly. I often do it while I'm riding (if I need to.) Another advantage is less chain/belt maintenance. As bad as this sounds, I haven't lubed my chain in a few months. I also haven't heard my chain in any of that time either. Not having to deal with shifting or a derailleur is very nice for the chain.

As for weight, I don't really notice it. The bike rides great when it's unloaded. Loaded it's heavy, so it doesn't matter.

For me, using an IGH is a matter of "what do you NEED it for." I commute year round, and often in bad conditions. I wanted a low maintenance drivetrain that wouldn't freeze in snow and sub zero temperatures. That's why I got an IGH. Otherwise a derailleur works just fine.