I have a 156 Selespeed, 2001 vintage with Momo leather. She's going soon ( she has been good as gold, 88,000 trouble free miles!) and I will be getting a diesel facelift 156 for my next Alfa!
A question though - I test drove such a 2.4 a couple of weeks ago and I was disappointed to find that the leather seats had fake leather backs - my seats are leather all over! Do all the facelift 156's with leather have seats like this?
I would look at getting a diesel with no leather and swapping your interiors over. Not a big job thes seats are very easy to remove althrough door cards take a while longer. You would probably save alot more on the new car than you would lose selling yours with a cloth interior.
Unfortunately the majority of 'leather' car seats nowadays have vinyl borders and backs. This even applies to most current Jaguars on the roads, but to be fair modern day vinyls age extremely well and have better wear characteristics than most leathers.