I lower mine all the time even though I don't need to for height purposes. When I first bought it the old owner said he never bothered adjusting the height, and when I toggled up and down a couple of times a bag went bang. When I replaced them there was absolutely no suppleness in them at all, and rightly or wrongly I've always believed if you don't keep them moving then they firm up.

Might be rubbish but it makes me feel like I'm keeping them loose and in good nick

I always used to put mine in extended height when washing it so I could clean the bags

Good idea. I wonder if its worth spraying the bags with Silicone spray to help protect them and keep them supple too? it would at least cut down on abrasion I'm guessing, and it shouldn't attract dirt?

^^^^^^
I do  2012 TDV8 Black Edition
2000 Disco. TD5
1975 series III