I think having an older sedan like a W126 is not only a matter of having enough cash, but some people, like me, just like them!!!
Call me crazy, but I would not trade my car straight up for a brand new one. With the exhaust situation, yeah, if yours is nearing its end anyways, by all means upgrade to a euro setup. It would end up costing around the same anyways. Are you wanting a stock euro setup (cat, resonator, OE muffler) or are you wanting to go more performance than that? For stock, just go with timevalve, but if you want to go further than that, I would get a custom bent setup, so you won't waste your money on the cat resonator and muffler if you're just going to get rid of them or replace them anyways. As far as the manifolds...hmm...try Potomac (pgauto.com) they sometimes have euro parts, but not always. It helps when you have a german connection, let me tell ya! I don't really know where specifically you could get a set...anyone have any ideas?