I guess it would have made a tiny bit of financial sense just after R230 was launched and I guess there was a big gap between the price of a R129 and R230. If you really really wanted a R230 but only had about 25k you could justify it, now its pretty much good for spares.
Using today's Autotrader prices a 2 year old SL is £40k and a 10 year old one is £10K.
I find myself struggling with this theory
As a general rule cars like this generally only exist because of a smash up. (In general) and here is how it goes
So the car is involved on a smash, you take it to the garage for repairs and find out that putting the car back to original, using original parts is going to be big money, someone suggests that turning into a r230 look alike would cost a similar amount but would make it seem like a much newer car.
Every time I see a car like this I just move on. What's the point
As for the point of not being able to afford a r230 so then using the money to turn an r129 into r230 doesn't work. It may look like a r230 but in truth it's still an r129 so you haven't bought a r230 for r129 money, what you do have is an r129 that has very little appeal (only a select group would be interested)
At the end of it you have an r129 that you have spent thousands on and is now worth less than an original r129.
Plus you look like a nob.
On a final note, the 25k you mention above would have got you a seriously good motor. Maybe not a brand new R230 but something special.
My dream car is a Ferrari F355 but I wouldnt buy a Toyota MR2 and fit a kit because It's not a Ferrari F355 just like the R129 is not the R230 it's a complete waste of time and money and you still end up with the other car that you didn't want.
If you really want a r230 and can't afford one the either save up until the price drops until you can or accept that we can't always get what we want, it's part of life