Regarding owning a W126, whichever model, I think the benifits far outweigh the cost as long as you find the 'right' car. My insurence dropped over $800 a year from my Saab, my property taxes also dropped significantly. The 420 is a pleasure to work on and as long as its is maintained at its current level it will never devalue though I don't intend to sell it.
Best of all, it loves to be driven. When I bought my first car out of school I made the typical young guys mistake, got a convertible sportscar and paid heavily for it. It was horribly expensive to maintain, miserable to work on, not to mention noisy and unsafe on the highway. I have a longish 45min-1 hour commute each way and now that is a silent restful experience. After a grueling 14 hour day I didn't want to zip and weave in traffic, I just want to cruise and unwind. I used to dread my commute and now I cherish it. How strange is that??
Don't worry too much, whichever choice you make, you've already made the right one.
Best of luck,
1988 420SEL 170K