Just an opinion...but the Catalina still will have a lot of depreciation left in her as a 2 year old. A 20 year old cat34 is worth about 50K...so you are looking at roughtly 80-100k of depreciation alone. Not much depreciation left in an old boat so that gives a lot of room for repairs and maintenance on the Tartan and of course you would have repairs on a Catalina over 20 years as well. One thing you won't have on a newer Catalina is blisters so if the Tartan hasn'tbeen treated you might want to reserve some bucks for that in your calculations...but otherwise, one might expect the Tartan to hold up a bit better over time due tothe intial fitting out quality.
So...on a purely financial basis...my guess is that the Tartan will cost you less over the long haul.