You should stick to metal as nylon will not spread the load, if you're wanting to protect the bodywork, you could sandwich large nylons ones in there too.
Just giving my opinion - I was really disappointed with the buffeting around my torso / shoulders on my 08 GS when I first got it and ended up fitting the winglets - a really noticeable improvement - the best mod/accessory I've added so far (looking forward to fitting my HID's this week though!). As for the problem drilling holes, I can't see how that's likely to affect the value unless you balls it up . Winglets would I think be generally recognised by most prospective buyers as one of those 'good to have' accessories, whilst the sticky thread on this section 'fitting winglets' provides really good quality info on how to do it and do a decent job. It managed to stop a hamfisted sod like me from going wrong anyway. As always just an opinion.....
Thanks for the opinions I think I will order some.
As for the shoes, I have bought some in the past that fit at the time but hurt me later, therefore if somebody had "given me their opinion first" I maybe wouldn't have bought them saving blisters and money.