With alll due respect Angus, most dampers are used to limit both bump and rebound travel and are therefore subjected to considerable loads often shock loads!
Having been involved in designing and making prototype dampers in the past there is no real difference between a plain damper body and a coil over body such as the one in Ronnie's picture.
If the 'ends' are falling off that is more likely to be they way they have been mounted to the chassis and would likely fail if they were just being used as dampers.
The cost of converting stock mini dampers to coil overs would make a cheap option but it would be unlikely that the damper manufacturer would service (rebuild) them when they wore out so you'd have to make another set! Most coil over manufacturers will service their dampers.
Also mini damping would not match the haynes roadster as the effective spring rates would be different and as the dampers would be non-adjustable the handling could be interesting to say the least.
Adjustable mini dampers arn't much cheaper than the coil overs specified for the haynes roadster which are the most logical choice, - You'll end up getting them in the end anyway so why not start out right to begin with!
As for spring rates there are many spring lengths and sizes for coil overs so that wouldn't be a problem but matching the damping rates to the spring is. (something that is eliminated with adjustable and rebuildable coil over dampers such as AVO or GAZ.)
It also never ceases to amaze me how many people skimp on tyres and dampers, the two things that will make or break the cars roadholding while spending 1000's of bucks on tuned engines......
Colin Chapman designed the original Seven to light and nimble with good roadholding and modest power, using the superior roadholding to beat morepowerful cars of the day.
To my mind spending money on good suspension, brakes and tyres yealds greater rewards than a tuned engine and that tuned engine can always be added later when funds allow.
I would however agree with ronnie that coil overs are overpriced but that's generally because most coil overs are sold to race teams for single seaters so you have to pay race car prices - but then AFAICS you get what you pay for and I'd pay for good roadholding.....
BV.
