Of course it won't, but spending £1000 on the suspension of a £2,000 E36 isn't going to make it worth £3,000. You're going to add a few hundred pounds onto the value at the most, and that isn't taking into account what having decent E46s in a similar price range might do the values.
I think suggesting that he'll get most of the money back is a bit off of the mark.
Sorry, that wasn't what I mean't.
You very very rarely get a return on mods on a car, certainly almost NEVER pound for pound !
I was referring to the car not suddenly becoming worth pennies after doing the work. Anyone buying a 10-15 year old car should realise suspension replacement is almost as mandatory as doing an oil change!
I'd be interested to see what you end up doing and what success you have as a result of that. Worst case you'll have a car that at the end of it should sell a bit quicker as its had a full suspension refresh.