I would spend as little as possible to get it in ridable condition and then enjoy the heck out of it. Think of it as a two-wheeled version of a bucket-T from the 50's: use lots of elbow grease, naval jelly & polish or paint on the bright work and the least amount of $$ because you probably won't get your money back out of it if you try to make it good as or better than new. In fact, I did a quick Google on "vista duo" and there's someone with a pristine, very original model on Craigslist in Boise who's got it listed for $300. That's probably the upper end for this type of a tandem. Even when it was new it would have sold for something less than the very nice Schwinn Town & Country tandems @ $175.00 back in the early 60's. I can't imagine how much time and effort it would take to get yours in that condition, but I suspect it would cost a lot more than $250 in labor and materials... unless you're not worried about the value of time.

Here's the deal, I don't believe it really has a lot of intrinsic value as a 'collector item' other than being an example a low- to mid-end cruiser tandem from the 60's, similar in quality and value to what you'd find at a department store today. In fact, you'll also find examples of Columbia-branded "Twosome" tandems that use the exact same frame from the same time period that you can use as a gauge for value (not to mention as a source for parts). Therefore, the value must be tied to what else you could buy to replace it for what ever your intended purpose was, e.g., just fun to go riding, as part of a display, a nostalgic acquisition, just a fun project bike to hone your restoration skills.

By the way, the cranks are fine the way they are... that's what's referred to as being set out of phase. While the vast majority of tandems you'll see have their cranks in-phase (crank arms aligned), there is an entire school of thought and practice out there that suggests riding out-of-phase can be as good or more efficient than in-phase. You change phasing by removing the chain from the idler wheel to create slack, and then reposition the front cranks chain ring on the chain so that they are either in line with or at a 90 degree angle from the rear cranks.