1. Is not worth dealing with Ron's drawbacks, IMO. Just go talk to them directly. I'm sure they'll be more than happy to talk with Harry Potter.
2. D&D has spells that remove insanity. Heal, Restoration, and Wish are all possibles. Other fictional magics may also allow it. This has been a subject of repeated discussion.
3. We would carry around many of the Horcruxes because the are in valuable magical items that we'd rather not destroy outright. Salazar Slytherin's Locket and Helga Hufflepuff's Cup are both noted to have magical powers and Rowena Ravenclaw's Diadem is noted to increase the wearer's wisdom. Why destroy irreplaceable artifacts like that when we could just used D&D Exorcise to kick the pieces of Voldemort's soul out of the objects and keep them?
4. And I'm saying that it's an incident of him being useful where we have viable alternatives available that don't involve us having to deal with Ron's drawbacks.
All things we can get from other people who don't have his drawbacks. I'm not denying any of the above, but it's not enough for me to want to invest time in Ron. There are far more interesting characters I'd prefer to invest our efforts into.
You mean other than dealing with his laziness, insecurity, immaturity, insensitivity, and all that entails? You may think his problems are worth dealing with for the benefits he gives, but I don't.
Yup -
http://harrypotter.wikia.com/wiki/Ronald_Weasley
He's not lazy 100% of the time, but most of the time he'll do things the easy way. Do you think he's going to be willing to put on weights, do pushups for hours, and practice his Occlumency so that Snape doesn't read his mind? I don't.